**Description**

Currently `BaseOperator` and `XComArgs` implements the same logic of `__lshift__`, `__rshift__` and others "chain" operations (`>>`, `<<`). It seems resonable to abstract this logic into `TaskMixin` to introduce some DRYness especially because the new concept of `TaskGroup` will also implement the same methods.

**Use case / motivation**

Limit duplication of logic.

**Related Issues**

https://github.com/apache/airflow/pull/10827#issuecomment-691927501
#10153 

airflow/models/baseoperator.py
t1.set_downstream(t2)
        t1.set_downstream(t3)
        t2.set_downstream(t4)
        t3.set_downstream(t5)
        t4.set_downstream(t6)
        t5.set_downstream(t6)
    :param tasks: List of tasks or List[airflow.models.BaseOperator] to set dependencies
    :type tasks: List[airflow.models.BaseOperator] or airflow.models.BaseOperator
    """
    for index, up_task in enumerate(tasks[:-1]):
        down_task = tasks[index + 1]
        if isinstance(up_task, BaseOperator):
            up_task.set_downstream(down_task)
            continue
        if isinstance(down_task, BaseOperator):
            down_task.set_upstream(up_task)
            continue
        if not isinstance(up_task, Sequence) or not isinstance(down_task, Sequence):
            raise TypeError(
                'Chain not supported between instances of {up_type} and {down_type}'.format(
                    up_type=type(up_task), down_type=type(down_task)))
        up_task_list = up_task
        down_task_list = down_task
        if len(up_task_list) != len(down_task_list):
            raise AirflowException(
                f'Chain not supported different length Iterable '
                f'but get {len(up_task_list)} and {len(down_task_list)}')
        for up_t, down_t in zip(up_task_list, down_task_list):
            up_t.set_downstream(down_t)
def cross_downstream(from_tasks: Sequence[BaseOperator],