[Bug #21094] Update nested module names when setting temporary name

	[Bug #21159] module names should not be modifiable

	Fix a bug in rb_include_module that stops nested inclusion into module subclasses

	This bug was present since the code was originally added by me
	in 3556a834a2847e52162d1d3302d4c64390df1694.

	Fixes [Bug #20871]

Fix crash when checking symbol encoding

	[Bug #20245]

	We sometimes pass in a fake string to sym_check_asciionly. This can crash
	if sym_check_asciionly raises because it creates a CFP with the fake
	string as the receiver which will crash if GC tries to mark the CFP.

	For example, the following script crashes:

	    GC.stress = true
	    Object.const_defined?("\xC3")

fix leak in module clone

Co-authored-by: Peter Zhu <peter@peterzhu.ca>

fix memory leak in vm_method

This introduces a unified reference_count to clarify who is referencing a method.
This also allows us to treat the refinement method as the def owner since it counts itself as a reference

Co-authored-by: Peter Zhu <peter@peterzhu.ca>

[Bug #19894]

When a copy of a complemented method entry is created, there are two
issues:

1. IMEMO_FL_USER3 is not copied, so the complemented status is not
   copied over.
2. In rb_method_entry_clone we increment both alias_count and
   complemented_count. However, when we free the method entry in
   rb_method_definition_release, we only decrement one of the two
   counters, resulting in the rb_method_definition_t being leaked.

Co-authored-by: Adam Hess <adamhess1991@gmail.com>

[Bug #19550]

If !RCLASS_EXT_EMBEDDED (e.g. 32 bit systems) then the rb_classext_t is
allocated throug malloc so it must be freed.

The issue can be seen in the following script:

```
20.times do
  100_000.times do
    mod = Module.new
    Class.new do
      include mod
    end
  end

  # Output the Resident Set Size (memory usage, in KB) of the current Ruby process
  puts `ps -o rss= -p #{$$}`
end
```

Before this fix, the max RSS is 280MB, while after this change, it's
30MB.

* Fix temporary methods on Object leaking across test cases.
* Remove temporary classes/modules leaking across test cases.