When we spill a register that we know contains only 32 interesting bits
and then reload it from the spill slot, it's enough to reload its lower
half. This may save a few bytes, and guards against accidental changes
to the upper half (e.g. via pointer decompression).

Bug: v8:13216
Change-Id: I1d950d6e33d8ae94cf385af4f3e1db028bf333c5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3854506Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82704}