Real implementations for apple_framework, apple_application, and apple_test_bundle

The apple_framework, apple_application, and apple_test_bundle target kinds are now real Starlark implementations instead of schema-only stubs. apple_framework emits a signed dylib with modulemap and Info.plist; apple_application links a Mach-O executable, embeds dependency frameworks, and can be launched with once run; apple_test_bundle produces an .xctest bundle and supports XCTest and Swift Testing through the generic once test capability. Some advanced features, such as resource bundling, asset catalogs, and custom entitlements, are still declared in the schema but not yet implemented.