Exception variables can be Object (e.g. throw 4) so loosen the type from
HeapObject.

Bug: v8:9810
Change-Id: I14600978ed5159b2b661bd09e69ad6d6530553ed
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1906566
Commit-Queue: Dan Elphick <delphick@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64861}