Collect all property definitions that are redefinition in self

Property definitions

nitc :: model_collect $ MClassDef :: collect_redef_mpropdefs
	# Collect all property definitions that are redefinition in `self`
	fun collect_redef_mpropdefs(filter: nullable ModelFilter): Set[MPropDef] do
		var res = new HashSet[MPropDef]
		for mpropdef in mpropdefs do
			if mpropdef.is_intro then continue
			if filter == null or filter.accept_mentity(mpropdef) then res.add mpropdef
		end
		return res
	end
src/model/model_collect.nit:1063,2--1071,4