Real implementations for apple_framework, apple_application, and apple_test_bundle

The previously schema-only Apple bundle target kinds are now backed by real build actions. apple_framework builds a signed .framework with dylib, modulemap, and Info.plist. apple_application produces a signed .app bundle, embeds framework dependencies, and can be launched with once run. apple_test_bundle produces a real .xctest bundle that can run via the generic Once test capability. Several attributes (e.g., resources, asset catalogs, entitlements, non-ad-hoc signing) are declared in the schema but are not yet implemented and will fail analysis if used.