Fix Emscripten warnings by removing deprecated writeAsciiToMemory (#2724)

The Emscripten function writeAsciiToMemory has been deprecated and logs
warnings
during the build process.

- Replaced usages of writeAsciiToMemory in wabt.post.js with TextEncoder
- Fixed a 1-byte buffer overflow in allocateCString
- Removed writeAsciiToMemory from CMake EXPORTED_RUNTIME_METHODS

Author: kevmoo

CMakeLists.txt

@@ -830,7 +830,7 @@ if (EMSCRIPTEN)
     -sALLOW_MEMORY_GROWTH
     -sEXPORT_ES6
     -sEXPORT_NAME=WabtModule
-    -sEXPORTED_RUNTIME_METHODS=writeAsciiToMemory
+    -sEXPORTED_RUNTIME_METHODS=stringToNewUTF8,lengthBytesUTF8
     -Oz
   )
   string(REPLACE ";" " " LIBWABT_LINK_FLAGS_STR "${LIBWABT_LINK_FLAGS}")