fix: cleanup public api of platform-server

BREAKING CHANGE: Parse5Adapter is no longer exported as public API, use serverBootstrap()

Parse5Adapter is an implementation detail not a public API

Closes #9237

Closes #9205

modules/@angular/platform-server/index.ts

@@ -1,2 +1 @@
-// TODO: vsavkin add SERVER_PROVIDERS and SERVER_APP_PROVIDERS
-export {Parse5DomAdapter} from './src/parse5_adapter';
+export {SERVER_PLATFORM_PROVIDERS, serverBootstrap, serverPlatform} from './src/server';