PR# 19983 Conversion queries: formal generic parameter convert type

The compiler should forbid the case where the convert type of a conversion query is a formal generic parameter.

For example in the example below, class `BB` declares a conversion query of the form `f: {G}` where `G` is a formal generic parameter. But for the actual generic derivation `BB [ANY]` we end up with an ambiguous behavior with `BB [ANY]` which both conforms and converts to `ANY`.

--
Eric Bezault

class AA

create

	make

feature

	make
		local
			b: BB [ANY]
			a: ANY
		do
			create a
			create b.make (a)
			a := b
		end

end
~~~~
class BB [G -> ANY]

create

	make

convert

	f: {G}

feature

	make (a: G)
		do
			attr := a
		end

	f: G
		do
			Result := attr
		end

	attr: G

end
~~~~
class CC

end