This CL re-implements Array.p.lastIndexOf in Torque. The implementation
consists of a generic baseline path and a fast-path for JSArrays with fast
ElementsKinds.

Sparse support for JSArrays was removed.

Bug: v8:7624
Change-Id: I6ae877aaf99fa97a91763b3d60a0ee05623ab085
Reviewed-on: https://chromium-review.googlesource.com/1190345
Commit-Queue: Simon Zünd <szuend@google.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55451}