StoreField wasn't emitting a write barrier after performing the store,
leading to the usual set of hard-to-debug issues. Now it does.

The write barrier requires some of its registers to be in fixed
locations, and others to be clobberable. Thsi patch extends the
temporaries mechanism to allow requesting a specific temporary, in this
case for the slot address scratch register.

Bug: v8:7700
Change-Id: I506856071e0f44feafb98c2685ef1b3362b0e41e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3613388
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80263}