A new CSA function, MoveElements() does an efficient memmove
operation when the ElementsKind or new-space status allows it.

A few other TNode cleanups applied in the file, for example,
preferring the StoreFixedDoubleArrayHole() function.

Change-Id: Ia0848c066eebbbbe321f81afe0cfa7df7567cbb7
Reviewed-on: https://chromium-review.googlesource.com/c/1268235
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56567}