bpo-39957: Change Signature.parameters to OrderedDict (GH-18988)

diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index 8a2efc8..f193807 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -2077,7 +2077,7 @@
         P = inspect.Parameter
 
         self.assertEqual(str(S()), '()')
-        self.assertEqual(repr(S().parameters), 'mappingproxy({})')
+        self.assertEqual(repr(S().parameters), 'mappingproxy(OrderedDict())')
 
         def test(po, pk, pod=42, pkd=100, *args, ko, **kwargs):
             pass
@@ -3181,6 +3181,11 @@
         l = list(signature.parameters)
         self.assertEqual(l, unsorted_keyword_only_parameters)
 
+    def test_signater_parameters_is_ordered(self):
+        p1 = inspect.signature(lambda x, y: None).parameters
+        p2 = inspect.signature(lambda y, x: None).parameters
+        self.assertNotEqual(p1, p2)
+
 
 class TestParameterObject(unittest.TestCase):
     def test_signature_parameter_kinds(self):