Huge functions can take a really long time (several minutes) in register
allocation. This is caused by a big number of virtual registers combined
with a big number of blocks.
We can avoid such long-running register allocation by falling back to
the mid-tier register allocation if we detect a huge number of virtual
registers.
Note that this is mostly relevant for bigger WebAssembly modules, but we
implement it as a general TurboFan flag.

The flag is off by default for now, since there seem to be bugs lurking
in the mid-tier register allocator. Once those are fixed, we can stage
it behind --future and then ship it.

R=mslekova@chromium.org
CC=thibaudm@chromium.org

Bug: v8:12320
Change-Id: Iff14de456c2b3a91ee2b2b12221295dd56b69463
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3231336Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77461}