GetFreeRegisters is supposed to find some number of free registers that
the current node can use as safe temporaries, but they shouldn't be
considered "allocated", as they will be free as soon as the node's code
completes.

Now we no longer decrement free_register_count_ in GetFreeRegisters, to
avoid leaking registers allocated for temporaries.

Bug: v8:7700
Change-Id: I485607fedec79fbeca4675781923b7ad3a6bfc6b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3497381Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79319}