Baseline write barrier needs to use different page flag mask to also
call into the slow path of the barrier for old-to-shared pointers.

Bug: v8:11708
Change-Id: I955f30376f3de912b418298cdcf1e38dd2adda2e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3834254
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82538}