PR# 19984 Conversion queries: generic convert types with same base class

The validity rule VYCQ-4 does not allow two convert types from conversion queries to have the same base class.
But EiffelStudio fails to report this validity rule.

In the example below, class `BB [G]` declares two conversion queries of the form `f: {CC [INTEGER]}` and `g: {CC [G]}`, but the two convert types have the same base class. This violates VYCQ-4. Indeed, for the actual generic derivation `BB [INTEGER]` there is an ambiguity between `f` and `g`.

--
Eric Bezault

class AA

create

	make

feature

	make
		local
			b: BB [INTEGER]
			c: CC [INTEGER]
		do
			create b
			c := b
		end

end
~~~~
class BB [G]

convert

	f: {CC [INTEGER]},
	g: {CC [G]}

feature

	f: CC [INTEGER]
		do
			create Result
		end

	g: CC [G]
		do
			create Result
		end

end
~~~~
class CC [G]

end