We need to use MachineRepresentation to properly distinguish
the types in compiler::UnallocatedOperand.

Bug: v8:7700
Change-Id: I4273512a00290bb85b09aeb3788643e346be03f7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3602515Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80140}