8202471: Resolves generic receiver type for types with generic signatures

[Rafael Winterhalter]

Hello,

I have created a patch such that getReceiverType() returns a parameterized
type if the receiver type declaration is itself generic. Currently, the
receiver type is always a type representation of Class such that
annotations on the type variables or the receiver type's owner type cannot
be resolved: https://gist.github.com/raphw/a155d5ef66d11e5fb131b7e6b8fb10e5

Note that this change can potentially break existing code if callers of the
method expect this behavior for parameterized receiver types. However,
without this change, the type information is lost and I would argue that
the current behavior can be considered to be incorrect.

Best regards, Rafael