Type resolution: Add support for enclosing methods and constructors

[ljacqu]

Classes can be inside methods and, strangely enough, inside constructors:

    private <T> MainClass() {
        class Foo {
            private T elem;
        }
    }

As in the example, there might be type information to get from there. This issue is about extending TypeVariableResolver#registerTypes to not just consider the enclosing class but enclosing methods and constructors, too.

Note that initializer blocks may also contain local classes.