handle builtins types in annotations with __allow_unmapped__

handle builtins types in annotations with __allow_unmapped__

Fixed issue with ``__allow_unmapped__`` declarative option where types that
were declared using collection types such as ``list[SomeClass]`` vs. the
typing construct ``List[SomeClass]`` would fail to be recognized correctly.
Pull request courtesy Pascal Corpet.

Fixes: #10385
Closes: #10390
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/10390
Pull-request-sha: f8796965aefc1852d4b1137d04bf811072a1a0e9

Change-Id: I114d29c3c076386508300e979371b0d760b761c7