LiveNodeInfo was stored in a Node->LiveNodeInfo map, which was never
copied or merged alongside control flow. Lookups in this map were a bit
part of register allocation time, and it was mostly duplicating data
that was already in the ValueNode.

So, instead of a separate LiveNodeInfo, store the current register
allocation state directly on the ValueNode. This involves a bit of
clobbering of state (in particular, we have to clobber the next_use id),
but that doesn't matter since regalloc is a forward pass and with this
change, it's less memory and zero map lookups.

Measuring on a (very large) function, this reduces compile time from
300ms to 200ms.

Bug: v8:7700
Change-Id: I02620f1a795bd308d1de03d694c102cb5ea3ff50
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3500617Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79339}