This updates the existing special casing of assignment operators by
gcmole to match for assignments of {HeapObject} instead of {HeapObject*}
variables. The former now uses the implicit C++ assignment operator call
instead of a primitive assignment binary operation.

Also removes the dead {handle_decl_name} field as a drive-by-fix.

R=mslekova@chromium.org
BUG=v8:8813

Change-Id: I0b48254e7ca1544bc064707a8ca1f204366ddbe4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1517879
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60212}