Enables the CocoaPods-based plugin workflow for macOS. This allows a
macOS project to automatically fetch and add native plugin
implementations via CocoaPods for anything in pubspec.yaml, as is done
on iOS.
- Removes SYMROOT from the Generated.xcconfig. Having it causes current
versions of Xcode to switch the project's build output to "Legacy",
which causes anything not overridden to use a project-relative build
directory instead of a shared directory in DerivedData, breaking
anything with subprojects that it depends on.
This means that `flutter run` and builds from Xcode will use
completely different build directories, but that each should be
internally consistent.
- Moves the FlutterMacOS.framework to $SRCROOT/Flutter. This is
consistent with the approach we're moving to for all desktop
platforms, and avoids issues finding it now that SYMROOT doesn't match
for the two different build modes.
Fixes#32494
