Fix for assignment check with type vars and OaM

[WolframPfeifer]

This PR fixes a bug in the assignment check, where fields of an @Any object could be assigned even though -Alint=checkOaM was activated. The cause was a missing use of effective annotations.

Minimal example where the bug occurs (I can add a test case if desired):

class IntCell {
  int f;
}

class L<T extends @Any IntCell> {
  void m(T x) {
    x.f = 5;  // should not be allowed with OaM, but the checker does not complain
  }
}

Note:

• This builds on my other PRs, Annotations for some PrintStream methods  #120 and Updated Readme with Linter Options for Encapsulation Checks (OaM) #123, which should be merged first.
• I am not sure if there is a corresponding case in the inference checker ...