This commit fixes how the language service evaluates the compatibility
of types to work with arbitrary union types. As a result, compatibility
checks are now more strict and can catch similarities or differences
more clearly.
```
number|string == string|null // OK
number|string == number // OK
number|string == null // not comparable
number == string // not comparable
```
Using Ivy as a backend should provide these diagnoses for free, but we
can backfill them for now.
Closes https://github.com/angular/vscode-ng-language-service/issues/723
PR Close#36529
8be0972836