This replaces InNewSpace with InYoungGeneration, which is
a prerequisite for young large objects.

Additional changes:
- FROM_SPACE, TO_SPACE flags are renamed to FROM_PAGE, TO_PAGE.
- A new LARGE_PAGE flag is added.
- The external string table is refactored to track young string
  instead of new space strings.

Bug: chromium:924547
Change-Id: Ia4e3ba1b72995c3400257a1f98559f091533e811
Reviewed-on: https://chromium-review.googlesource.com/c/1437274Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59156}