- Unroll loop in ReadVarInt to skip checks for uncommon branches and
  improve by ~15%
- Use cage_base more aggressively
- Use more dehandlified code if possible
- Allow allocating strings directly in old-space to avoid filling up the
  new space when deserialising web-snapshots

Cleanup:
- ThrowDataCloneError now returns Nothing<bool>() for more consistency

Bug: v8:11525
Change-Id: I69ac635e2bcab83e92fba5ab34603146fa21f043
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3437049Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78999}