CheckedFloat64Unbox mutates the input value, but the register allocator
does not expects this behaviour and propagates a wrong value in the register.
In particular we deopt with the wrong value if the second Float64Unbox
in a Float64Add needs to deopt.

This fixes the input value after we convert to double.

Bug: v8:7700
Change-Id: Ib89573e9f728dc3a34b817fc84f1afcb96f14d18
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3610422
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Auto-Submit: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80214}