LoadKind is not longer just for load, we use it for stores as well
(starting with https://crrev.com/c/2473383). Rename it to something more
generic.

Bug: v8:10975,v8:10933
Change-Id: I5e5406ea475e06a83eb2eefe22d4824a99029944
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2481822
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70626}