[monodroid] C++ tweaks and legacy code cleanup (#8638)

Remove old and unused code originally written for:

  * Classic Xamarin.Android
  * [Xamarin.Android Designer][0] on Windows
  * Xamarin.Android Designer on macOS

Remove a collection of platform and compiler compatibility macros,
typedefs and wrapper functions.

Migrate from `char` arrays to `std::string_view` for more strongly
typed code.

Move `-fstack-clash-protection` from `LOCAL_COMMON_COMPILER_ARGS` to
`LOCAL_COMMON_LINKER_ARGS`; it's a linker flag.

Use `#pragma clang diagnostic ignored "-Warray-bounds"` around
certain "MonoVM-isms" in the GC bridge to silence array bounds
checking warnings.

Refactor to use new(er) C++ types such as `std::span`, `std::array`,
and `std::string_view`.  This helps reduce memory allocations in some
scenarios, allows usage of the newer `for (e : collection)` syntax,
and increases type safety.

[0]: https://github.com/MicrosoftDocs/xamarin-docs/blob/ff833dc5af413e10802afca108212c0a7b2d6fa2/docs/android/user-interface/android-designer/designer-basics.md

src/monodroid/CMakeLists.txt

@@ -322,6 +322,16 @@ endif()
 # Compiler and linker flags
 set(LINK_LIBS "")
 
+#
+# -Wformat-nonliteral is disabled as it's not very practical, because we use proxy functions to
+# pass formats to the final Android logger functions. The Android functions have attributes that
+# cause warnings similar to:
+#
+#  warning G4FD2E6FD: format string is not a string literal [-Wformat-nonliteral]
+#
+# The warning is, in general, a good practice because the compiler can verify the printf format
+# at compile time, but in our case it's not very useful.
+#
 set(LOCAL_COMMON_COMPILER_ARGS
   -Wall
   -Wconversion
@@ -333,6 +343,7 @@ set(LOCAL_COMMON_COMPILER_ARGS
   -Wextra
   -Wformat-security
   -Wformat=2
+  -Wno-format-nonliteral
   -Wimplicit-fallthrough
   -Wmisleading-indentation
   -Wnull-dereference
@@ -341,7 +352,6 @@ set(LOCAL_COMMON_COMPILER_ARGS
   -Wsign-compare
   -Wtrampolines
   -Wuninitialized
-  -fstack-clash-protection
   -fstrict-flex-arrays=3
   )
 
@@ -370,6 +380,10 @@ endif()
 
 set(LOCAL_COMMON_LINKER_ARGS "")
 if(ANDROID)
+  list(APPEND LOCAL_COMMON_LINKER_ARGS
+    -fstack-clash-protection
+  )
+
   if (ENABLE_CLANG_ASAN OR ENABLE_CLANG_UBSAN)
     list(APPEND LOCAL_COMMON_COMPILER_ARGS
       -fno-omit-frame-pointer