There were multiple bugs and no test coverage for br_on_cast and br_on_cast_fail, specifically for the paths in the decoder where those
checks get optimized away.

Bug: v8:7748
Change-Id: I6e5d6449152df0456b43938174f57055a4c63fdd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3723503Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81349}