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 bytes to free up one bit from the offset.

All changes are deactivated behind the build flag
`v8_enable_pointer_compression_8gb`. Allocation folding is not yet
supported.

Bug: v8:13070
Change-Id: I602c71232e98eac4e2701b0922704a7adc31a662
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3817741
Commit-Queue: Teo Dutu <teodutu@google.com>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82331}