builtins.filter compat with typing.TypeGuard (#6726)

This change enables the following use-case:
```python
def is_not_none(x: Optional[int]) -> TypeGuard[int]:
    return x is not None

list_optional: list[Optional[int]] = [0, None, 1, None, 2]
generate_ints: Iterable[int] = filter(is_not_none, list_optional)
```

Co-authored-by: Alex Waygood <[email protected]>

Author: Jasha10

stdlib/builtins.pyi

@@ -1065,6 +1065,8 @@ class filter(Iterator[_T], Generic[_T]):
     @overload
     def __init__(self, __function: None, __iterable: Iterable[_T | None]) -> None: ...
     @overload
+    def __init__(self, __function: Callable[[_S], TypeGuard[_T]], __iterable: Iterable[_S]) -> None: ...
+    @overload
     def __init__(self, __function: Callable[[_T], Any], __iterable: Iterable[_T]) -> None: ...
     def __iter__(self) -> Iterator[_T]: ...
     def __next__(self) -> _T: ...