gh-119180: Fix annotationlib.ForwardRef.evaluate with no globals (#124326)

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.

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>