Rather than macos/Flutter containing a mixture of files that should and
shouldn't be checked in, create clear locations for:
- Files that are "owned" by Flutter, but should be checked in
(Flutter/). This will contain files like the top-level Flutter
xcconfigs, generated plugin registrants, etc.
- Files that are generated by Flutter on the fly, and should not be
checked in (Flutter/ephemeral/). This will contain Flutter SDK caches,
the generated xcconfig, etc.
Also adds Flutter-owned Debug and Release xcconfig variants, in
preparation for PodSpec tooling.
- 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
