…onlib module scope

We were sometimes passing None as the globals argument to eval(), which makes it
inherit the globals from the calling scope. Instead, ensure that globals is always
non-None. The test was passing accidentally because I passed "annotationlib" as a
module object; fix that. Also document the parameters to ForwardRef() and remove
two unused private ones.

…s and eval()

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>