Join the text of all visited tokens

Property definitions

nitc :: parser_work $ Prod :: collect_text
	# Join the text of all visited tokens
	fun collect_text: String
	do
		var v = new TextCollectorVisitor
		v.enter_visit(self)
		assert v.text != ""
		return v.text
	end
src/parser/parser_work.nit:166,2--173,4