**Apache Airflow version**:

2.0.1

**What happened**:

When clearing task across dags using `ExternalTaskMarker` the dag state of the external `DagRun` is not set to active. So cleared tasks in the external dag will not automatically start if the `DagRun` is a Failed or Succeeded state.

**What you expected to happen**:

The external `DagRun` run should also be set to Running state.

**How to reproduce it**:

Clear tasks in an external dag using an ExternalTaskMarker.


**Anything else we need to know**:

Looking at the code is has:

https://github.com/apache/airflow/blob/b23fc137812f5eabf7834e07e032915e2a504c17/airflow/models/dag.py#L1323-L1335

It seems like it intentionally calls the dag member method `set_dag_run_state` instead of letting the helper function `clear_task_insntances` set the `DagRun` state. But the member method will only change the state of `DagRun`s of dag where the original task is, while I believe `clear_task_instances` would correctly change the state of all involved `DagRun`s.

tests/sensors/test_external_task_sensor.py
op1.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, ignore_ti_state=True)
        
        op2 = ExternalTaskSensor(
            task_id='test_external_task_sensor_check_delta_2',
            external_dag_id=TEST_DAG_ID,
            external_task_id=TEST_TASK_ID,
            execution_date_fn=lambda dt: dt + timedelta(days=1),
            allowed_states=['success'],
            timeout=1,
            poke_interval=1,
            dag=self.dag,
        )
        with pytest.raises(exceptions.AirflowSensorTimeout):
            op2.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, ignore_ti_state=True)
    def test_external_task_sensor_fn_multiple_args(self):
        """Check this task sensor passes multiple args with full context. If no failure, means clean run."""
        self.test_time_sensor()
        def my_func(dt, context):
            assert context['execution_date'] == dt
            return dt + timedelta(0)
        op1 = ExternalTaskSensor(
            task_id='test_external_task_sensor_multiple_arg_fn',
            external_dag_id=TEST_DAG_ID,
            external_task_id=TEST_TASK_ID,
            execution_date_fn=my_func,
            allowed_states=['success'],
            dag=self.dag,
        )
        op1.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, ignore_ti_state=True)
    def test_external_task_sensor_fn_kwargs(self):