By maintaining a separate list of registers that can't be freed we can
keep track of decisions already made for a node, and avoid creating
conflicts. This can be used to avoid freeing fixed input/temporary
requirements or other assigned registers.

Bug: v8:7700
Change-Id: I3c24e0502e66714cf5f68374811741bc9f5e8b21
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3714242Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81268}