This adds the following:
1) Heap object structure classes: RawHeap, BaseArena and BasePage.
   - freelist
   - linear allocation block
2) ObjectAllocator, a class responsible for object (and page) allocation.

The design doc with UML design: https://bit.ly/2VVTcqc

User defined arenas are followup.

Bug: chromium:1056170
Change-Id: I69a82974bd08e3cf3da90041b1628297cc890891
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2167392
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67425}