Add __new__ to str and int stubs in both Pythons. (#1352)

* Update default values to `...` in `__init__` and `__new__` in `int` and `str`.
* Add `__new__` to `enum.IntEnum` to override inherited `__new__`.
* Add `type: ignore` comment to `IntEnum`

stdlib/3/builtins.pyi

@@ -103,7 +103,16 @@ class super:
     def __init__(self) -> None: ...
 
 class int(SupportsInt, SupportsFloat, SupportsAbs[int]):
-    def __init__(self, x: Union[SupportsInt, str, bytes] = ..., base: int = ...) -> None: ...
+    @overload
+    def __init__(self, x: SupportsInt = ...) -> None: ...
+    @overload
+    def __init__(self, x: Union[str, bytes], base: int = ...) -> None: ...
+
+    @overload
+    def __new__(cls: Type[_T1], x: SupportsInt = ...) -> _T1: ...
+    @overload
+    def __new__(cls: Type[_T1], x: Union[str, bytes], base: int = ...) -> _T1: ...
+
     def bit_length(self) -> int: ...
     def to_bytes(self, length: int, byteorder: str, *, signed: bool = ...) -> bytes: ...
     @classmethod
@@ -227,11 +236,15 @@ class complex(SupportsAbs[float]):
 
 class str(Sequence[str]):
     @overload
-    def __init__(self) -> None: ...
+    def __init__(self, o: object = ...) -> None: ...
     @overload
-    def __init__(self, o: object) -> None: ...
+    def __init__(self, o: bytes, encoding: str = ..., errors: str = ...) -> None: ...
+
     @overload
-    def __init__(self, o: bytes, encoding: str = ..., errors: str = 'strict') -> None: ...
+    def __new__(cls: Type[_T1], o: object = ...) -> _T1: ...
+    @overload
+    def __new__(cls: Type[_T1], o: bytes, encoding: str = ..., errors: str = ...) -> _T1: ...
+
     def capitalize(self) -> str: ...
     def casefold(self) -> str: ...
     def center(self, width: int, fillchar: str = ' ') -> str: ...