Adds support for non-simple fp aliasing (e.g., Arm) for the fast
register allocator.

BUG=v8:9684

Change-Id: I6717ef1c6cb4e585fa4b6ea8cea7087e68f441e9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2300483
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69198}