Both LO_SPACE and NEW_LO_SPACE use the basic page management system of
LargeObjectSpace, but implement different AllocateRaw methods (with
the NEW_LO_SPACE version shadowing the LO_SPACE version).

To clean this up, and allow other future LargeObjectSpace implementations
(in particular, an off-thread variant), refactored the current
LargeObjectSpace into a base class, and make both LargeObjectSpace
(renamed to OldLargeObjectSpace) and NewLargeObjectSpace extend this
class.

Bug: chromium:1011762
Change-Id: I41b45b97f2611611dcfde677213131396df03a5e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1876824
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64560}