This is a reland of 6c65e858

Changes since revert:

- Add --disable-shared-ro-heap-for-testing flag that is implied by
  d8's --stress-snapshot, since RO heap sharing currently
  does not support deserializing/serializing while original Isolate
  is still running
- Add BUILD.gn assert that v8_enable_pointer_compression_shared_cage
  requires x64 or arm64

Original change's description:
> [ptr-cage] Turn on shared pointer cage by default for arm64 and x64
>
> Bug: v8:11460
> Change-Id: I9ab419b5e90fbe677e1d63b41699d90552839e98
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2873226
> Commit-Queue: Shu-yu Guo <syg@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#74422}

Bug: v8:11460
Change-Id: I7eb189b7f8ac3e30da96b0dadd2c085f08a1a0b1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2878855
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74448}