GCMole mistakenly thought that GC guards such as DisallowHeapAllocation
covered the whole scope of the function they are declared in. This CL
fixes the false negatives and adds appropriate testing.

Bug: v8:10071
Change-Id: Iffb369977af90ca053a55ca8f451e037a4f460f2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2497451
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70763}