Drive-by-fix:
- Use explicit casts to HeapNumber in NumberToXXX methods

Bug: v8:11263
Change-Id: If99af3ccee33a299d9f42cd39b87b6935a555f83
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3512618Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79438}