This PR changes the language service to work in two different modes:
1. TS + Angular
Plugin augments TS language service to provide additonal Angular
information. This only works with inline template and is meant to be
used as a local plugin (configured via tsconfig.json).
2. Angular only
Plugin only provides information on Angular templates, no TS info at
all. This effectively disables native TS features and is meant for
internal use only.
Default mode is `angularOnly = false` so that we don't break any users
already using Angular LS as local plugin.
As part of the refactoring, `undefined` is removed from type aliases
because it is considered bad practice.
go/tsstyle#nullableundefined-type-aliases
```
Type aliases must not include |null or |undefined in a union type.
Nullable aliases typically indicate that null values are being passed
around through too many layers of an application, and this clouds the
source of the original issue that resulted in null. They also make it
unclear when specific values on a class or interface might be absent.
```
PR Close#31935
cran-cg
Keen Yee Liau
Alan
Keen Yee Liau
Frederik Prijck
Chuck Jazdzewski
Tobias Bosch
Victor Berchet
Miško Hevery
Jason Aden