Previously, StoreStoreElimination handled allocations as
"can observe anything". This is pretty conservative and prohibits
elimination of repeated double stores to the same field.
With this CL allocations are changed to "observes initializing or
transitioning stores".
This way it is guaranteed that initializing stores to a freshly created
object or stores that are part of a map transition are not eliminated
before allocations (that can trigger GC), but allows elimination of
non-initializing, non-transitioning, unobservable stores in the
presence of allocations.

Bug: v8:12200
Change-Id: Ie1419696b9c8cb7c39aecf38d9f08102177b2c0f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3295449
Commit-Queue: Patrick Thier <pthier@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78230}