**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
else:
                raise e
        dag_id = TEST_DAG_ID
        dag = DAG(dag_id, default_args=self.args, schedule_interval=timedelta(minutes=1))
        task_without_failure = ExternalTaskSensor(
            task_id='task_without_failure',
            external_dag_id=dag_external_id,
            external_task_id='task_external_without_failure',
            execution_date_fn=lambda dt: [dt + timedelta(seconds=i) for i in range(2)],
            allowed_states=['success'],
            retries=0,
            timeout=1,
            poke_interval=1,
            dag=dag,
        )
        task_with_failure = ExternalTaskSensor(
            task_id='task_with_failure',
            external_dag_id=dag_external_id,
            external_task_id='task_external_with_failure',
            execution_date_fn=lambda dt: [dt + timedelta(seconds=i) for i in range(2)],
            allowed_states=['success'],
            retries=0,
            timeout=1,
            poke_interval=1,
            dag=dag,
        )
        task_without_failure.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, ignore_ti_state=True)
        with pytest.raises(AirflowSensorTimeout):
            task_with_failure.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE, ignore_ti_state=True)
    def test_external_task_sensor_delta(self):