[Checkers] Modification to AnnotatedTypeVariable and AnnotatedWildcardType

[Michael Ernst]

Mahmood-

I don't see anything wrong with your proposal (but I haven't carefully read
the specifications of the given methods).

Is it ever necessary to know whether an annotation is directly on a
typevar/wildcard or not?  Your proposal seems to make that distinction
impossible to determine.  (In our type systems, typevars/wildcards are not
allowed to be annotated, so it wouldn't hurt us, but do other designs where
it's sensible exist?)

                    -Mike