Collect all properties inehrited by self

Property definitions

nitc :: model_collect $ MClass :: collect_inherited_mproperties
	# Collect all properties inehrited by `self`
	fun collect_inherited_mproperties(mainmodule: MModule, filter: nullable ModelFilter): Set[MProperty] do
		var set = new HashSet[MProperty]
		for parent in collect_parents(mainmodule, filter) do
			set.add_all(parent.collect_intro_mproperties(filter))
			set.add_all(parent.collect_inherited_mproperties(mainmodule, filter))
		end
		return set
	end
src/model/model_collect.nit:762,2--770,4