FlutterMacOS.framework engine isn't natively available for desktop for ARM macOS Apple Sillicon (including building for all valid architectures on x86)

`FlutterMacOS.framework` only contains x86_64 architecture, so desktop apps run with Rosetta translation.  Add `arm64` to the framework.

See also
https://chromium.googlesource.com/chromium/src/+/refs/heads/master/docs/mac_arm64.md