Change the following in the `flutter create` templates. I didn't make any auto-migrations for existing apps because none seem that critical:
1. Turn on `ASSETCATALOG_COMPILER_GENERATE_SWIFT_ASSET_SYMBOL_EXTENSIONS` in iOS and macOS.
1. Turn on `BuildIndependentTargetsInParallel` in macOS template. https://github.com/flutter/flutter/pull/125827/files#r1181817619
1. Turn on `DEAD_CODE_STRIPPING` in macOS template.
1. Set `ENABLE_USER_SCRIPT_SANDBOXING=NO` in iOS and macOS template. `flutter` scripts don't work with this on. This might require a migration in the future to explicitly turn this one off. However at least for now if the setting isn't present it defaults to `NO`.
Add migration for `LastUpgradeVersion` so users won't see these validation issues in Xcode.
Run migrator on all the example apps. A few aren't Flutter apps so I edited them in Xcode.
Fixes https://github.com/flutter/flutter/issues/140253
See also https://github.com/flutter/flutter/issues/125817 and https://github.com/flutter/flutter/pull/90304.
1. Add iOS and macOS migration to mark "last upgraded" Xcode version to 14.3 to prevent `Update to recommended settings` warning.
2. Update iOS and macOS templates to same.
3. Update iOS template to set `BuildIndependentTargetsInParallel` to YES as suggested. I didn't add a migration for this since it seems like a minor optimization and I don't think it's worth a potentially botched/corrupted migration.
4. Run all example/integration test project to see migrator work.
5. Add some missing test projects to the build shard since I noticed they were missing and I had to build those manually outside `SHARD=build_tests`.
Fixes https://github.com/flutter/flutter/issues/125817
See https://github.com/flutter/flutter/pull/90304 for Xcode 13 example.
Move Flutter Gallery to dev/integration_tests/ as it is an older copy used only for testing. The current version of the Flutter Gallery now lives in https://github.com/flutter/gallery.
