[Bugfix] Fix method visibility in some corner cases

[itarato]

We've been seeing some inconsistencies between truffle/cruby on how added method visibility is derived: #3134

Related Ruby issue: https://bugs.ruby-lang.org/issues/19749

Expectation

• if define target == current callFrame self -> use scope visibility
• use public visibility

This PR is fixing these cases:

Redefine private method but outside of its context (should be public)

class Foo10
	private

	def bar
		"public"
	end
end

foo10 = Foo10.new
foo10.define_singleton_method(:bar, foo10.method(:bar))

foo10.bar # No error in CRuby but fails in TruffleRuby

Redefine public method in the same context as private (should be private)

class Foo11
	def bar; end
end

foo11 = Foo11.new

class << foo11
	private
	
	define_method(:bar, Foo11.new.method(:bar))
end

foo11.bar # Fails in CRuby but no errors in TruffleRuby

[eregon]

@andrykonchin had a very related fix in #3187 for issue #3181.
@andrykonchin Could you rebase this? I think the code changes can be dropped because they seem to do the same and then it's just extra specs, which is valuable.

[eregon]

Let's use a local variable here, I don't think this class needs to be named.
@andrykonchin Could you do that?

[andrykonchin]

Merged in f5c5c19