Move some methods to transitions-inl.h to avoid using methods defined
in other inl headers.

R=verwaest@chromium.org

Bug: v8:7965
Change-Id: I0f5a97ffa4c5faad1687c1586ef2dbf5193939bb
Reviewed-on: https://chromium-review.googlesource.com/c/1303299
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57080}