functionality is:
If rhs_is_smi is true, we are sure that rhs is a Smi.
If rhs_is_smi is false, rhs might or not be a Smi.

Therefore, rhs_known_smi fits better.

Change-Id: Ie6dd0446ef85ba0730189e2012a21c24d1731b74
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1796551Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63669}