Jump gap moves (for phis and register merges) are emitted as a parallel
move (i.e. treated as a single mapping from registers to registers and
emitted in a way that they don't clobber each other). However, the phi
input allocation was updating the register state as if they were
serialised moves (i.e. a list of moves, one after the other, where each
move could clobber another move's input).

Now the jump phi initialisation doesn't update register state.

Bug: v8:7700
Change-Id: Iecf3211d59d9c416a4449aea22fef633717d92d3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3784983Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81934}