TurboShaft is a new, CFG-based IR for TurboFan.
This CL adds the basic IR and bidirectional translation from/to
TurboFan's sea-of-nodes-based IR for some common operators (still
incomplete even for JS).

Bug: v8:12783
Change-Id: I162fdf10d583a9275a9f655f5b44b888faf813f6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3563562Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80136}