- block regs that already contained the value
- clear the blocklists (including double) in more places
- check that a ForceAllocated reg isn't blocked yet (when allocated
  at start)

Bug: v8:7700
Change-Id: I17b58ff23e0558f962a5d798a39ebb7d9b0ae634
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3716470Reviewed-by: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81273}