Add string marshallers for ANSI and platform-defined

[elinor-fung]

• Update to latest test packages
  • Needed so that we reference a version of the framework assemblies that have OperatingSystem.IsWindows()
• Add marshallers for handling CharSet.Ansi/UnmanagedType.LPStr and CharSet.Auto
  • They offload a bunch of the actual generation to the UTF-8 and UTF-16 marshallers and only partially participate in the conditional stackalloc logic.
• Add tests

Ran on Windows and Linux (patched with the fix for component loading in muxer mode). Did not run on macOS.

cc @AaronRobinsonMSFT @jkoritzinsky

Ansi

public static partial string Method_Ansi(string p, in string pIn, ref string pRef, out string pOut)
{
    unsafe
    {
        pOut = default;
        string __retVal;
        //
        // Setup
        //
        byte *__retVal_gen_native;
        byte *__p_gen_native;
        bool p__allocated = false;
        byte *__pIn_gen_native;
        bool pIn__allocated = false;
        byte *__pRef_gen_native;
        byte *__pOut_gen_native;
        //
        // Marshal
        //
        if (System.OperatingSystem.IsWindows())
        {
            __p_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemAnsi(p);
        }
        else
        {
            if (p == null)
            {
                __p_gen_native = null;
            }
            else
            {
                int p__bytelen = (p.Length + 1) * 3 + 1;
                if (p__bytelen > 260)
                {
                    __p_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemUTF8(p);
                    p__allocated = true;
                }
                else
                {
                    byte *p__stackptr = stackalloc byte[p__bytelen];
                    {
                        p__bytelen = System.Text.Encoding.UTF8.GetBytes(p, new System.Span<byte>(p__stackptr, p__bytelen));
                        p__stackptr[p__bytelen] = 0;
                    }

                    __p_gen_native = (byte *)p__stackptr;
                }
            }
        }

        if (System.OperatingSystem.IsWindows())
        {
            __pIn_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemAnsi(pIn);
        }
        else
        {
            if (pIn == null)
            {
                __pIn_gen_native = null;
            }
            else
            {
                int pIn__bytelen = (pIn.Length + 1) * 3 + 1;
                if (pIn__bytelen > 260)
                {
                    __pIn_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemUTF8(pIn);
                    pIn__allocated = true;
                }
                else
                {
                    byte *pIn__stackptr = stackalloc byte[pIn__bytelen];
                    {
                        pIn__bytelen = System.Text.Encoding.UTF8.GetBytes(pIn, new System.Span<byte>(pIn__stackptr, pIn__bytelen));
                        pIn__stackptr[pIn__bytelen] = 0;
                    }

                    __pIn_gen_native = (byte *)pIn__stackptr;
                }
            }
        }

        if (System.OperatingSystem.IsWindows())
        {
            __pRef_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemAnsi(pRef);
        }
        else
        {
            __pRef_gen_native = null;
            if (pRef != null)
            {
                __pRef_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemUTF8(pRef);
            }
        }

        //
        // Invoke
        //
        __retVal_gen_native = Method_Ansi__PInvoke__(__p_gen_native, &__pIn_gen_native, &__pRef_gen_native, &__pOut_gen_native);
        //
        // Unmarshal
        //
        if (System.OperatingSystem.IsWindows())
        {
            __retVal = __retVal_gen_native == null ? null : new string ((sbyte *)__retVal_gen_native);
        }
        else
        {
            __retVal = System.Runtime.InteropServices.Marshal.PtrToStringUTF8((System.IntPtr)__retVal_gen_native);
        }

        if (System.OperatingSystem.IsWindows())
        {
            pRef = __pRef_gen_native == null ? null : new string ((sbyte *)__pRef_gen_native);
        }
        else
        {
            pRef = System.Runtime.InteropServices.Marshal.PtrToStringUTF8((System.IntPtr)__pRef_gen_native);
        }

        if (System.OperatingSystem.IsWindows())
        {
            pOut = __pOut_gen_native == null ? null : new string ((sbyte *)__pOut_gen_native);
        }
        else
        {
            pOut = System.Runtime.InteropServices.Marshal.PtrToStringUTF8((System.IntPtr)__pOut_gen_native);
        }

        //
        // Cleanup
        //
        if (p__allocated)
        {
            System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__p_gen_native);
        }

        if (pIn__allocated)
        {
            System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__pIn_gen_native);
        }

        System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__pRef_gen_native);
        System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__pOut_gen_native);
        return __retVal;
    }
}

[System.Runtime.InteropServices.DllImportAttribute("DoesNotExist", CharSet = System.Runtime.InteropServices.CharSet.Ansi, EntryPoint = "Method_Ansi")]
extern private static unsafe byte *Method_Ansi__PInvoke__(byte *p, byte **pIn, byte **pRef, byte **pOut);

Auto

public static partial string Method_Auto(string p, in string pIn, ref string pRef, out string pOut)
{
    unsafe
    {
        pOut = default;
        string __retVal;
        //
        // Setup
        //
        void *__retVal_gen_native = null;
        void *__p_gen_native = null;
        bool p__allocated = false;
        void *__pIn_gen_native = null;
        bool pIn__allocated = false;
        void *__pRef_gen_native = null;
        void *__pOut_gen_native = null;
        //
        // Marshal
        //
        if (!System.OperatingSystem.IsWindows())
        {
            if (p == null)
            {
                __p_gen_native = null;
            }
            else
            {
                int p__bytelen = (p.Length + 1) * 3 + 1;
                if (p__bytelen > 260)
                {
                    __p_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemUTF8(p);
                    p__allocated = true;
                }
                else
                {
                    byte *p__stackptr = stackalloc byte[p__bytelen];
                    {
                        p__bytelen = System.Text.Encoding.UTF8.GetBytes(p, new System.Span<byte>(p__stackptr, p__bytelen));
                        p__stackptr[p__bytelen] = 0;
                    }

                    __p_gen_native = (byte *)p__stackptr;
                }
            }
        }

        if (System.OperatingSystem.IsWindows())
        {
            if (pIn == null)
            {
                __pIn_gen_native = null;
            }
            else
            {
                int pIn__bytelen = (pIn.Length + 1) * 2;
                if (pIn__bytelen > 520)
                {
                    __pIn_gen_native = (ushort *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemUni(pIn);
                    pIn__allocated = true;
                }
                else
                {
                    byte *pIn__stackptr = stackalloc byte[pIn__bytelen];
                    ((System.ReadOnlySpan<char>)pIn).CopyTo(new System.Span<char>(pIn__stackptr, pIn__bytelen));
                    __pIn_gen_native = (ushort *)pIn__stackptr;
                }
            }
        }
        else
        {
            if (pIn == null)
            {
                __pIn_gen_native = null;
            }
            else
            {
                int pIn__bytelen = (pIn.Length + 1) * 3 + 1;
                if (pIn__bytelen > 260)
                {
                    __pIn_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemUTF8(pIn);
                    pIn__allocated = true;
                }
                else
                {
                    byte *pIn__stackptr = stackalloc byte[pIn__bytelen];
                    {
                        pIn__bytelen = System.Text.Encoding.UTF8.GetBytes(pIn, new System.Span<byte>(pIn__stackptr, pIn__bytelen));
                        pIn__stackptr[pIn__bytelen] = 0;
                    }

                    __pIn_gen_native = (byte *)pIn__stackptr;
                }
            }
        }

        if (System.OperatingSystem.IsWindows())
        {
            __pRef_gen_native = null;
            if (pRef != null)
            {
                __pRef_gen_native = (ushort *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemUni(pRef);
            }
        }
        else
        {
            __pRef_gen_native = null;
            if (pRef != null)
            {
                __pRef_gen_native = (byte *)System.Runtime.InteropServices.Marshal.StringToCoTaskMemUTF8(pRef);
            }
        }

        //
        // Invoke
        //
        fixed (char *__p_gen_native__pinned = p)
        {
            __retVal_gen_native = Method_Auto__PInvoke__(System.OperatingSystem.IsWindows() ? (ushort *)__p_gen_native__pinned : __p_gen_native, &__pIn_gen_native, &__pRef_gen_native, &__pOut_gen_native);
        }

        //
        // Unmarshal
        //
        if (System.OperatingSystem.IsWindows())
        {
            __retVal = __retVal_gen_native == null ? null : new string ((char *)__retVal_gen_native);
        }
        else
        {
            __retVal = System.Runtime.InteropServices.Marshal.PtrToStringUTF8((System.IntPtr)__retVal_gen_native);
        }

        if (System.OperatingSystem.IsWindows())
        {
            pRef = __pRef_gen_native == null ? null : new string ((char *)__pRef_gen_native);
        }
        else
        {
            pRef = System.Runtime.InteropServices.Marshal.PtrToStringUTF8((System.IntPtr)__pRef_gen_native);
        }

        if (System.OperatingSystem.IsWindows())
        {
            pOut = __pOut_gen_native == null ? null : new string ((char *)__pOut_gen_native);
        }
        else
        {
            pOut = System.Runtime.InteropServices.Marshal.PtrToStringUTF8((System.IntPtr)__pOut_gen_native);
        }

        //
        // Cleanup
        //
        if (p__allocated)
        {
            System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__p_gen_native);
        }

        if (pIn__allocated)
        {
            System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__pIn_gen_native);
        }

        System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__pRef_gen_native);
        System.Runtime.InteropServices.Marshal.FreeCoTaskMem((System.IntPtr)__pOut_gen_native);
        return __retVal;
    }
}

[System.Runtime.InteropServices.DllImportAttribute("DoesNotExist", CharSet = System.Runtime.InteropServices.CharSet.Auto, EntryPoint = "Method_Auto")]
extern private static unsafe void *Method_Auto__PInvoke__(void *p, void **pIn, void **pRef, void **pOut);

[AaronRobinsonMSFT]

LGTM.