- Fix tracing of reference return values. StoreTaggedPointer should not
  use the write barrier since we are writing to the stack.
- Avoid re-allocating a slot for the return value when it is already
  spilled.

R=manoskouk@chromium.org

Change-Id: I6418c48332964a1c3d407abafaf466b0e789be69
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3882971
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83102}