Fixes#15528
What is the current behavior?
The language service access TypeScript's Symbol.members without checking for null or undefined.
What is the new behavior?
The access is guarded.
In v2.x, users had to annotate classes that they intended to use as tokens with `@Injectable`. This is no longer required in v4.x for tokens,
and we now require the constructor parameters of classes annotated
with `@Injectable` to be statically analyzable by ngc.
This commit reduces the error into a warning
if the constructor parameters do not meet this condition.
DEPRECATION:
- Classes annotated with `@Injectable` but whose constructor’s parameter types
are not statically analyzable by ngc will produce a warning.
Closes#15003
