`Fiber#raise` recursively raises on nested resuming_fiber. (#10482)

	* Improve consistency of `Fiber.current.raise`.

	Enumerator should use a non-blocking fiber, change `rb_fiber_new` to be non-blocking by default. (#10481)

When a forked process was started in a thread, this would result in a
double-free during the child process exit.

    RUBY_FREE_AT_EXIT=1 ./miniruby -e 'Thread.new { fork { } }.join; Process.waitpid'

This is because the main thread in the forked process was not the
initial VM thread, and the new thread's stack was freed as part of
objectspace iteration.

This change also allows rb_threadptr_root_fiber_release to run without
EC being available.

Mostly just fixing RDoc's incorrect treatment of `+`

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>

* YJIT: Cancel on-stack jit_return on invalidation

Co-authored-by: Alan Wu <alansi.xingwu@shopify.com>

* Use RUBY_VM_CONTROL_FRAME_STACK_OVERFLOW_P

---------

Co-authored-by: Alan Wu <alansi.xingwu@shopify.com>

To fix https://github.com/ruby/ruby/actions/runs/6581593578/job/17881779994

Contrary to my initial assumption, rb_threadptr_root_fiber_setup() is
called for each Ractor, not just once at boot. I changed the place to
call rb_jit_cont_init() to avoid calling it multiple times.