Maglev groups all its tagged spill slots together, and the number of
them doesn't change. This means that the generality of the existing
safepoint mechanism is massive overkill for maglev code.

This patch adds a maglev-specific safepoint table, which is the
safepoint of a code object if-and-only-if that code object has maglev
code. This safepoint stores the number of tagged and untagged slots
once, globally, and individual entries are just used for deopts and for
storing the state of pushed registers (this is currently unused, but
will be used in the future for pushing registers in deferred calls).

Bug: v8:7700
Change-Id: I15f84a6e957357825e84e33238f8a36f2e0b3012
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3747858
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81564}