In order to support a larger heap cage (8GB, 16GB), the cage offset
will take up more than 32 bits. As a consequence, for 8GB cages, the
least significant bit of the cage offset will overlap with the most
significant bit of the tagged offset. To avoid this, allocations need
to be aligned to 8 or 16 bytes to free up one or two bits from the
offset.

The allocation top is kept properly aligned without adding fillers in
the newly created gaps, by aligning allocation sizes to 8 bytes.

Bug: v8:13070
Change-Id: I169b51e583d7a4be61d2a6c6060fcf74b410703c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3877147Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Teo Dutu <teodutu@google.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83277}