Fixes a few issues with Windows text input:
- Filters out ASCII control characters
- Filters out lead surrogates, which aren't valid UTF-16 on their own so will cause assertion failures if sent to Flutter
- Adds a bandaid fix for a crash due to mismatches in indexing in the C++ and Dart text models. (A better fix would be to use UTF-16 and add surrogate pair handling to deletion and forward/back; that will be a later PR since it has a larger scope.)
Fixes https://github.com/flutter/flutter/issues/54879
Significantly improves the behavior of non-ASCII text input on Windows. Correctly
processes incoming character events as UTF-16, and for now uses UTF-32 for
the text model so that the existing index-based logic will work much more often.
Future work is still needed, but this will handle far more cases correctly.
Changes include:
- File structure
- Header guards
- Include paths
- Namespaces
- Integration with the engine's GN build
- Conversion from jsoncpp to rapidjson
- Style and clang-format adjustment to match engine repository
