when the RUBY_FREE_ON_SHUTDOWN environment variable is set, manually free memory at shutdown.

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>
Co-authored-by: Peter Zhu <peter@peterzhu.ca>

This solves multiple problems.

First, RB_VM_LOCK_ENTER/LEAVE is a barrier. We could at least use the
_NO_BARRIER variant.

Second, this doesn't need to interfere with GC or other GVL users when
multiple Ractors are used. This needs to be used in very few places, so
the benefit of fine-grained locking would outweigh its small maintenance
cost.

Third, it fixes a crash for YJIT. Because YJIT is never disabled until a
process exits unlike MJIT that finishes earlier, we could call jit_cont_free
when EC no longer exists, which crashes RB_VM_LOCK_ENTER.

* Make mjit_cont sharable with YJIT

* Update dependencies

* Update YJIT binding

This commit prevents the stack from being marked twice: once via the
Fiber, and once via the Thread.  It introduces an assertion to assert
that the ec on the thread is the same as the ec on the Fiber being
marked via the thread.

These contents are purely implementation details, not worth appearing in
CAPI documents. [ci skip]

* Rename `rb_scheduler` to `rb_fiber_scheduler`.

* Use public interface if available.

* Use `rb_check_funcall` where possible.

* Don't use `unblock` unless the fiber was non-blocking.

* Enables Mutex to be used as synchronization between multiple Fibers
  of the same Thread.
* With a Fiber scheduler we can yield to another Fiber on contended
  Mutex#lock instead of blocking the entire thread.
* This also makes the behavior of Mutex consistent across CRuby, JRuby and TruffleRuby.
* [Feature #16792]