
Convert `ProjectMigration.run()` and `ProjectMigrator.migrate()` to be async. Needed for Swift Package Manager migration, which requires some async processes: https://github.com/flutter/flutter/pull/146256
Convert `ProjectMigration.run()` and `ProjectMigrator.migrate()` to be async. Needed for Swift Package Manager migration, which requires some async processes: https://github.com/flutter/flutter/pull/146256