bpo-38659: [Enum] add _simple_enum decorator (GH-25285)

add:

_simple_enum decorator to transform a normal class into an enum
_test_simple_enum function to compare
_old_convert_ to enable checking _convert_ generated enums
_simple_enum takes a normal class and converts it into an enum:

@simple_enum(Enum)
class Color:
    RED = 1
    GREEN = 2
    BLUE = 3

_old_convert_ works much like _convert_ does, using the original logic:

# in a test file
import socket, enum
CheckedAddressFamily = enum._old_convert_(
        enum.IntEnum, 'AddressFamily', 'socket',
        lambda C: C.isupper() and C.startswith('AF_'),
        source=_socket,
        )

test_simple_enum takes a traditional enum and a simple enum and
compares the two:

# in the REPL or the same module as Color
class CheckedColor(Enum):
    RED = 1
    GREEN = 2
    BLUE = 3

_test_simple_enum(CheckedColor, Color)

_test_simple_enum(CheckedAddressFamily, socket.AddressFamily)

Any important differences will raise a TypeError

Lib/test/test_uuid.py

@@ -4,6 +4,7 @@ from test.support import import_helper
 import builtins
 import contextlib
 import copy
+import enum
 import io
 import os
 import pickle
@@ -31,6 +32,13 @@ def mock_get_command_stdout(data):
 class BaseTestUUID:
     uuid = None
 
+    def test_safe_uuid_enum(self):
+        class CheckedSafeUUID(enum.Enum):
+            safe = 0
+            unsafe = -1
+            unknown = None
+        enum._test_simple_enum(CheckedSafeUUID, py_uuid.SafeUUID)
+
     def test_UUID(self):
         equal = self.assertEqual
         ascending = []