With this CL we add support for all externref globals except for
imported mutable globals.

R=thibaudm@chromium.org

Bug: v8:7581
Change-Id: I63cb26f8ad6f4b8fc1c276e223c5d45745122ebf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2396086
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69741}