Collect all properties introduced in self

Property definitions

nitc :: model_collect $ MModule :: collect_intro_mproperties
	# Collect all properties introduced in `self`
	fun collect_intro_mproperties(filter: nullable ModelFilter): Set[MProperty] do
		var res = new HashSet[MProperty]
		for mclass in collect_intro_mclasses(filter) do
			res.add_all mclass.collect_intro_mproperties(filter)
		end
		return res
	end
src/model/model_collect.nit:585,2--592,4