Type the constructor of IntEnum and IntFlag (#5217)

These should only accept integers or enum members.

Author: arthaud

stdlib/enum.pyi

@@ -45,6 +45,7 @@ class Enum(metaclass=EnumMeta):
 
 class IntEnum(int, Enum):
     value: int
+    def __new__(cls: Type[_T], value: Union[int, _T]) -> _T: ...
 
 def unique(enumeration: _S) -> _S: ...
 
@@ -53,6 +54,7 @@ _auto_null: Any
 # subclassing IntFlag so it picks up all implemented base functions, best modeling behavior of enum.auto()
 class auto(IntFlag):
     value: Any
+    def __new__(cls: Type[_T]) -> _T: ...
 
 class Flag(Enum):
     def __contains__(self: _T, other: _T) -> bool: ...
@@ -65,6 +67,7 @@ class Flag(Enum):
     def __invert__(self: _T) -> _T: ...
 
 class IntFlag(int, Flag):
+    def __new__(cls: Type[_T], value: Union[int, _T]) -> _T: ...
     def __or__(self: _T, other: Union[int, _T]) -> _T: ...
     def __and__(self: _T, other: Union[int, _T]) -> _T: ...
     def __xor__(self: _T, other: Union[int, _T]) -> _T: ...