We don't ever want a node's type to become less precise.

Also move a part of JSTypedLowering::ReduceJSStrictEqual that
can be expressed solely in terms of types into the typer, where
it generalizes an existing case.

Change-Id: I37c58fed48f606f6fe34e98e5f066434e50cb6c1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2106204
Auto-Submit: Georg Neis <neis@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66763}