Processing StateValues into operands is one of the most costly
parts of instruction selection. As it happens, StateValues are
shared by many nodes, and so we are unecessarily reprocessing
the same StateValues multiple times. This CL introduces caching
for the processed StateValues enabling very fast emitting of
operands for subsiquent instructions with the same StateValue.
The hitrate for the cache is higher than 90% on most optimizations.

BUG=v8:9684

Change-Id: I7edcfa1b0d7add16e509f0e2abeda0a8873f5a95
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2756535
Auto-Submit: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73434}