We can use member initializers instead of the OTHER_CONSTANTS macro to
handle the declaration of oddball AstValue members in AstValueFactory.

Bug: v8:6921
Change-Id: I701e2fd36f854cfc0d835981d060622070b5bfba
Reviewed-on: https://chromium-review.googlesource.com/719395Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48611}