Fold the CheckHeapObject check into the other checks (CheckMaps,
CheckString, etc), to avoid emitting a separate IR node with separate
deopt info and a separate actual deopt point.

Allow this check to be elided when we already know the node is a heap
object.

Bug: v8:7700
Change-Id: I981860a6522c082d86abc856cfe1b3ff5658ac59
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3867733
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82912}