merge revision(s) 2cc7a56e,b0711b1,db5d9429: [Backport #20209]

	YJIT: Avoid leaks by skipping objects with a singleton class

	For receiver with a singleton class, there are multiple vectors YJIT can
	end up retaining the object. There is a path in jit_guard_known_klass()
	that bakes the receiver into the code, and the object could also be kept
	alive indirectly through a path starting at the CME object baked into
	the code.

	To avoid these leaks, avoid compiling calls on objects with a singleton
	class.

	See: https://github.com/Shopify/ruby/issues/552

	[Bug #20209]
	---
	 yjit/bindgen/src/main.rs       |  1 +
	 yjit/src/codegen.rs            | 17 +++++++++++++++++
	 yjit/src/cruby_bindings.inc.rs |  1 +
	 yjit/src/stats.rs              |  2 ++
	 4 files changed, 21 insertions(+)

	YJIT: Fix tailcall and JIT entry eating up FINISH frames (#9729)

	Suppose YJIT runs a rb_vm_opt_send_without_block()
	fallback and the control frame stack looks like:

	```
	will_tailcall_bar [FINISH]
	caller_that_used_fallback
	```

	will_tailcall_bar() runs in the interpreter and sets up a tailcall.
	Right before JIT_EXEC() in the `send` instruction, the stack will look like:

	```
	bar [FINISH]
	caller_that_used_fallback
	```

	Previously, JIT_EXEC() ran bar() in JIT code, which caused the `FINISH`
	flag to return to the interpreter instead of to the JIT code running
	caller_that_used_fallback(), causing code to run twice and probably
	crash. Recent flaky failures on CI about "each stub expects a particular
	iseq" are probably due to leaving methods twice in
	`test_optimizations.rb`.

	Only run JIT code from the interpreter if a new frame is pushed.
	---
	 test/ruby/test_optimization.rb | 11 +++++++++++
	 vm_exec.h                      |  3 ++-
	 2 files changed, 13 insertions(+), 1 deletion(-)

	YJIT: No need to RESTORE_REG now that we reject tailcalls

	Thanks to Kokubun for noticing.

	Follow-up: b0711b1cf152afad0a480ee2f9bedd142a0d24ac
	---
	 vm_exec.h | 1 -
	 1 file changed, 1 deletion(-)

I don't use that these days. I'd like to remove this to ease a change
I'm writing. I'll resurrect this when I need this again.

I closed https://github.com/ruby/ruby/pull/7543, but part of the diff
seems useful regardless, so I extracted it.

Use ISEQ_BODY macro to get the rb_iseq_constant_body of the ISeq. Using
this macro will make it easier for us to change the allocation strategy
of rb_iseq_constant_body when using Variable Width Allocation.

Now that we're using the jit function entry point, we don't need the
scraper.  Thank you for your service, scraper. ❤️

Renaming uJIT to YJIT. AKA s/ujit/yjit/g.