Fix a build break when using new GenApi (#5269)

- example failure in https://dev.azure.com/dnceng/internal/_build/results?buildId=601199
- undo a small part of #4585)
  - restore generation of `[StructLayout]` attributes on most value types
  - original commit was 1faec9a

src/Microsoft.Cci.Extensions/Writers/CSharp/CSDeclarationWriter.Types.cs

@@ -25,8 +25,7 @@ public void WriteTypeDeclaration(ITypeDefinition type)
             // But we need also consider if this attribute is filtered out or not but I guess
             // we have the same problem with all the fake attributes at this point.
 
-            if (type.IsClass && type.Layout != LayoutKind.Auto ||
-                type.IsStruct && (type.Layout != LayoutKind.Sequential || type.Alignment != 0 || type.SizeOf != 0 || type.StringFormat != StringFormatKind.Ansi))
+            if ((type.IsStruct || type.IsClass) && type.Layout != LayoutKind.Auto)
             {
                 FakeCustomAttribute structLayout = new FakeCustomAttribute("System.Runtime.InteropServices", "StructLayoutAttribute");
                 string layoutKind = string.Format("System.Runtime.InteropServices.LayoutKind.{0}", type.Layout.ToString());