Adds scroll event handling to the macOS shell, sending them using the
new embedding API.
Currently, trackpad scrolling is just handled like scrollwheel
scrolling, since the trackpad-gesture-based scroll handling in Flutter
is still in progress.
Adds code to synthesize Add events if mouse tracking isn't enabled,
so that it doesn't rely on Flutter being lenient about handling events
from pointers that have never been added.
Merges the current flutter-desktop-embedding macOS framework into the
engine. Notable changes:
- All channel/codec related code is eliminated in favor of using the
existing iOS implementations.
- All .m files renamed to .mm for consistency with the iOS code.
- Some minor code changes to fix new warnings in Objective-C++ mode.
- License headers, basic format (e.g., clang-format changes) updated to
use repo style.
- Xcode project is not included; instead adds GN build rules to create
an integrated framework that combines what was the FDE library with
what is present in FlutterEmbedder.framework.
Other changes are left as follow-ups, including:
- Moving shared code out of ios/ into common/.
- Potentially improving sharing between iOS and macOS BUILD.gn.
- Class renaming; the FLE prefix will be eliminated, but that API
surface isn't stable yet, so that can be changed later.
