Add support for non-nullable reference types.
Refactor the GetValueType function. Emit a meaningful
initializer for every ref type in globals instead of an
empty one. Avoid the non-nullable recursive type by only
allowing indices that are strictly less than the current index.

Bug: v8:11954
Change-Id: Id1a405525080de7eb9dbbd4f2b8aea5f05684665
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3251171
Commit-Queue: Maria Tîmbur <mtimbur@google.com>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77659}