bpo-40066: [Enum] update str() and format() output (GH-30582)

Undo rejected PEP-663 changes:

- restore `repr()` to its 3.10 status
- restore `str()` to its 3.10 status

New changes:

- `IntEnum` and `IntFlag` now leave `__str__` as the original `int.__str__` so that str() and format() return the same result
- zero-valued flags without a name have a slightly changed repr(), e.g. `repr(Color(0)) == '<Color: 0>'`
- update `dir()` for mixed-in types to return all the methods and attributes of the mixed-in type
- added `_numeric_repr_` to `Flag` to control display of unnamed values
- enums without doc strings have a more comprehensive doc string added
- `ReprEnum` added -- inheriting from this makes it so only `__repr__` is replaced, not `__str__` nor `__format__`; `IntEnum`, `IntFlag`, and `StrEnum` all inherit from `ReprEnum`

Lib/test/test_ssl.py

@@ -373,7 +373,8 @@ class BasicSocketTests(unittest.TestCase):
         # Make sure that the PROTOCOL_* constants have enum-like string
         # reprs.
         proto = ssl.PROTOCOL_TLS_CLIENT
-        self.assertEqual(str(proto), 'PROTOCOL_TLS_CLIENT')
+        self.assertEqual(repr(proto), '<_SSLMethod.PROTOCOL_TLS_CLIENT: 16>')
+        self.assertEqual(str(proto), '16')
         ctx = ssl.SSLContext(proto)
         self.assertIs(ctx.protocol, proto)
 
@@ -622,7 +623,7 @@ class BasicSocketTests(unittest.TestCase):
                 with self.assertWarns(DeprecationWarning) as cm:
                     ssl.SSLContext(protocol)
                 self.assertEqual(
-                    f'{protocol!r} is deprecated',
+                    f'ssl.{protocol.name} is deprecated',
                     str(cm.warning)
                 )
 
@@ -631,8 +632,9 @@ class BasicSocketTests(unittest.TestCase):
                 ctx = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
                 with self.assertWarns(DeprecationWarning) as cm:
                     ctx.minimum_version = version
+                version_text = '%s.%s' % (version.__class__.__name__, version.name)
                 self.assertEqual(
-                    f'ssl.{version!r} is deprecated',
+                    f'ssl.{version_text} is deprecated',
                     str(cm.warning)
                 )