When buildin an array boilerplate description, we currently walk the
array literal as if it had tagged pointers, and post-hoc copy it to
a FixedDoubleArray if it had double elements kind.

Now, we calculate the elements kind during the InitDepthAndFlags walk,
and if the elements kind is Double, we allocate a FixedDoubleArray to
start with, and convert the elements of the array literal directly to
unboxed doubles in the array.

Change-Id: I56561e0af2236e785498eb70cb37eddcb09a56ca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2002529
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65817}