**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.

airflow/models/taskinstance.py
registered = False
                try:
                    registered = task_copy.register_in_sensor_service(self, context)
                except Exception:  
                    self.log.warning(
                        "Failed to register in sensor service."
                        " Continue to run task in non smart sensor mode.",
                        exc_info=True,
                    )
                if registered:
                    
                    self._update_ti_state_for_sensing()
            
            with set_current_context(context):
                result = self._execute_task(context, task_copy)
            
            task_copy.post_execute(context=context, result=result)
        Stats.incr(f'operator_successes_{self.task.task_type}', 1, 1)
        Stats.incr('ti_successes')
    @provide_session
    def _update_ti_state_for_sensing(self, session=None):
        self.log.info('Submitting %s to sensor service', self)
        self.state = State.SENSING
        self.start_date = timezone.utcnow()
        session.merge(self)
        session.commit()
        
        raise AirflowSmartSensorException("Task successfully registered in smart sensor.")
    def _execute_task(self, context, task_copy):