Now that the Angular LS is a proper tsserver plugin, it does not make
sense for it to maintain its own language service API.
This is part one of the effort to remove our custom LanguageService
interface.
This interface is cumbersome because we have to do two transformations:
ng def -> ts def -> lsp definition
The TS LS interface is more comprehensive, so this allows the Angular LS
to return more information.
PR Close#31972
```
NgLSHost: AngularLanguageServiceHost
NgLS: AngularLanguageService
```
NgLSHost should not depend on NgLS, because it introduces circular
dependency.
Instead, the `getTemplateAst` and `getTemplatAstAtPosition` methods should
be moved to NgLSHost and exposed as public methods.
This removes the circular dependency, and also removes the need for the
awkward 'setSite' method in NgLSHost.
PR Close#31122
Keen Yee Liau
Ben Lesh
Alan
Miško Hevery
Jason Aden