flutter#31277: pass track widget creation flag through to build script

flutter#31218: Add run capability for macOS target

flutter#31205: Add desktop projects and build commands (experimental)

flutter#30670: Implement StandardMethodCodec for C++ shells

Framework Changes

In addition to platform specifics, we continue to push on the core of the Flutter framework.

engine#8402: Enable shutting down all root isolates in a VM.

flutter#31210: Use full height of the glyph for caret height on Android v2

flutter#30422: Commit a navigator.pop as soon as the back swipe is lifted

flutter#30792: Rename Border.uniform() -> Border.fromSide()