Having interrupt budget updates be part of register allocation caused
various difficulties around gap moves for temporaries vs. gap moves for
phis. This patch splits them off into a separate node which is
separately allocated, and adds invariant checks that phi-updating nodes
don't do any other tricky register allocation.

Bug: v8:7700
Change-Id: I5a454fe4c5a5adff08d5a327ee34fbb43cda97ce
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3751196Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81604}