When --maglev is set, tier up to Maglev from unoptimized tiers based on
--interrupt-budget-for-maglev, initially set to 40KB (which should very
roughly by 1/10th of the time until the TF tierup decision is made).
On the first interrupt, a non-concurrent optimization to Maglev is
requested, which the next call to the marked function will perform.

- There is no support for tiering from Maglev to TF yet.
- Maglev's language support is minimal and tests are not expected to
  pass with --maglev.
- Disable --maglev by default for now.

Drive-by: fixes related to Maglev flag definitions.

Bug: v8:7700
Change-Id: I121bb3f4f3830fdd20e1d4a12d3e04f08a99be38
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3500302Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79328}

Maglev is mid-tier optimising compiler designed mainly for compilation
speed that can still generate good code for straightforward JS.

This initial commit is an MVP for Maglev which can compile and run some
very simple code, and sets up a framework that we can build upon.

Design:
https://docs.google.com/document/d/13CwgSL4yawxuYg3iNlM-4ZPCB8RgJya6b8H_E2F-Aek/edit#

Bug: v8:7700
Change-Id: I5ae074ae099126c2c0d50864ac9b3d6fa5c9e85a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3483664Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79247}