This allows to replace redundant LoadField's whose type doesn't match
the type of the replacement, by just turning those LoadField's into
TypeGuard's.

Bug: v8:8070
Change-Id: Ia329bb536f8829be27e070e90e9eaae0618dac7a
Reviewed-on: https://chromium-review.googlesource.com/1188131Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55407}