Add an overload to the exec method with _Executable statement for update and delete statements

[joachimhuet]

I think we should add an overload to the exec method to still have the possibility of passing an _Executable statement:

    @overload
    def exec(
        self,
        statement: _Executable,
        *,
        params: Optional[Union[Mapping[str, Any], Sequence[Mapping[str, Any]]]] = None,
        execution_options: Mapping[str, Any] = util.EMPTY_DICT,
        bind_arguments: Optional[Dict[str, Any]] = None,
        _parent_execute_state: Optional[Any] = None,
        _add_event: Optional[Any] = None,
    ) -> TupleResult[_TSelectParam]:
        ...

Originally posted by @joachimhuet in #831 (comment)

[federicober]

This is also valid for insert statements