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/inspect.py

@@ -2567,15 +2567,21 @@ class _empty:
 
 
 class _ParameterKind(enum.IntEnum):
-    POSITIONAL_ONLY = 0
-    POSITIONAL_OR_KEYWORD = 1
-    VAR_POSITIONAL = 2
-    KEYWORD_ONLY = 3
-    VAR_KEYWORD = 4
+    POSITIONAL_ONLY = 'positional-only'
+    POSITIONAL_OR_KEYWORD = 'positional or keyword'
+    VAR_POSITIONAL = 'variadic positional'
+    KEYWORD_ONLY = 'keyword-only'
+    VAR_KEYWORD = 'variadic keyword'
 
-    @property
-    def description(self):
-        return _PARAM_NAME_MAPPING[self]
+    def __new__(cls, description):
+        value = len(cls.__members__)
+        member = int.__new__(cls, value)
+        member._value_ = value
+        member.description = description
+        return member
+
+    def __str__(self):
+        return self.name
 
 _POSITIONAL_ONLY         = _ParameterKind.POSITIONAL_ONLY
 _POSITIONAL_OR_KEYWORD   = _ParameterKind.POSITIONAL_OR_KEYWORD
@@ -2583,14 +2589,6 @@ _VAR_POSITIONAL          = _ParameterKind.VAR_POSITIONAL
 _KEYWORD_ONLY            = _ParameterKind.KEYWORD_ONLY
 _VAR_KEYWORD             = _ParameterKind.VAR_KEYWORD
 
-_PARAM_NAME_MAPPING = {
-    _POSITIONAL_ONLY: 'positional-only',
-    _POSITIONAL_OR_KEYWORD: 'positional or keyword',
-    _VAR_POSITIONAL: 'variadic positional',
-    _KEYWORD_ONLY: 'keyword-only',
-    _VAR_KEYWORD: 'variadic keyword'
-}
-
 
 class Parameter:
     """Represents a parameter in a function signature.