Instead of changing all of TryToName to do the conversion to array
index, this patch narrows this fast path just to the element load IC
handler.

This patch also restores the HeapNumber conversion in TryToIntPtr and
in Turbofan inlining as per the original state of things.

Bug: v8:9449, chromium:1016738, chromium:1016709
Change-Id: Ibf3a2c38637fc36e0ee037dc740f273848d1e8a5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1902386
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64896}