bpo-40792: Make the result of PyNumber_Index() always having exact type int. (GH-20443)

Previously, the result could have been an instance of a subclass of int.

Also revert bpo-26202 and make attributes start, stop and step of the range
object having exact type int.

Add private function _PyNumber_Index() which preserves the old behavior
of PyNumber_Index() for performance to use it in the conversion functions
like PyLong_AsLong().
diff --git a/Lib/test/test_copy.py b/Lib/test/test_copy.py
index 35f72fb..ba3d233 100644
--- a/Lib/test/test_copy.py
+++ b/Lib/test/test_copy.py
@@ -357,7 +357,7 @@
             pass
         tests = [None, 42, 2**100, 3.14, True, False, 1j,
                  "hello", "hello\u1234", f.__code__,
-                 NewStyle, Classic, max, property()]
+                 NewStyle, range(10), Classic, max, property()]
         for x in tests:
             self.assertIs(copy.deepcopy(x), x)
 
@@ -579,17 +579,6 @@
         self.assertIsNot(y, x)
         self.assertIs(y.foo, y)
 
-    def test_deepcopy_range(self):
-        class I(int):
-            pass
-        x = range(I(10))
-        y = copy.deepcopy(x)
-        self.assertIsNot(y, x)
-        self.assertEqual(y, x)
-        self.assertIsNot(y.stop, x.stop)
-        self.assertEqual(y.stop, x.stop)
-        self.assertIsInstance(y.stop, I)
-
     # _reconstruct()
 
     def test_reconstruct_string(self):