Return a new String instance for txt

Property definitions

nitc $ NaiveInterpreter :: string_instance
	# Return a new String instance for `txt`
	fun string_instance(txt: String): Instance
	do
		var nat = c_string_instance(txt)
		var res = self.send(self.force_get_primitive_method("to_s_unsafe", nat.mtype), [nat, self.int_instance(txt.byte_length), self.int_instance(txt.length), self.false_instance, self.false_instance])
		assert res != null
		return res
	end
src/interpreter/naive_interpreter.nit:379,2--386,4