gh-119180: Avoid going through AST and eval() when possible in annotationlib (#124337)

gh-119180: Avoid going through AST and eval() when possible in annotationlib (#124337)

Often, ForwardRefs represent a single simple name. In that case, we
can avoid going through the overhead of creating AST nodes and code
objects and calling eval(): we can simply look up the name directly
in the relevant namespaces.

Co-authored-by: Victor Stinner <vstinner@python.org>