Test wildcards in stub files. Fix unbounded wildcards in stub files.

[wmdietl]

This should fix typetools issue 3236.

[wmdietl]

@cpovirk FYI. Using <?> in .astub files now has the same meaning as in .java files - no extra restrictions. If the underlying bytecode had a restriction, it is removed.
Please let me know if this doesn't work as expected.

[cpovirk]

Thanks! I imagine this was prompted by collection-object-parameters-may-be-null.astub, as the original issue said. I don't remember what originally brought that to my attention, but I'll try out a real-world demo after we pull in the next upgrade.

[cpovirk]

I'm a little confused because I can't seem to reproduce the problem with collection-object-parameters-may-be-null.astub under 3.21.4-eisop1, which is before this fix:

ArrayBlockingQueue<String> l = new ArrayBlockingQueue<>(1);
List<@Nullable Object> other = Arrays.asList((Object) null);
boolean b = l.removeAll(other); // surprisingly no error

I seem to recall that JDK stubs are somehow "special"; maybe that explains why they were working before other stubs were?

Anyway, the fact that it's working is still good news. And it continues to work under 3.23.0-eisop2.