feat(compiler-cli): expose ngtsc as a TscPlugin (#28431)

This lets us run ngtsc under the tsc_wrapped custom compiler (Used in Bazel)
It also allows others to simply wire ngtsc into an existing typescript compilation binary

PR Close #28431

packages/compiler-cli/index.ts

@@ -24,3 +24,4 @@ export {CompilerOptions as AngularCompilerOptions} from './src/transformers/api'
 export {NgTools_InternalApi_NG_2 as __NGTOOLS_PRIVATE_API_2} from './src/ngtools_api';
 
 export {ngToTsDiagnostic} from './src/transformers/util';
+export {NgTscPlugin} from './src/ngtsc/tsc_plugin';