This CL is an initial attempt to reuse BoundedPageAllocator for cppgc.
The caged 4GB heap is needed for:
- fast implementation of the generational barrier;
- potential pointer compression project for Oilpan.

Bug: chromium:1029379
Change-Id: Idfb0ab92c988e2045d4a0e9746bedf841d66e282
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2215818
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68074}