**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/dag.py
self,
        date_last_automated_dagrun: Optional[pendulum.DateTime],
    ) -> Tuple[Optional[pendulum.DateTime], Optional[pendulum.DateTime]]:
        """
        Get information about the next DagRun of this dag after ``date_last_automated_dagrun`` -- the
        execution date, and the earliest it could be scheduled
        :param date_last_automated_dagrun: The max(execution_date) of existing
            "automated" DagRuns for this dag (scheduled or backfill, but not
            manual)
        """
        if (
            self.schedule_interval == "@once" and date_last_automated_dagrun
        ) or self.schedule_interval is None:
            
            return (None, None)
        next_execution_date = self.next_dagrun_after_date(date_last_automated_dagrun)
        if next_execution_date is None:
            return (None, None)
        if self.schedule_interval == "@once":
            
            return (next_execution_date, next_execution_date)
        return (next_execution_date, self.following_schedule(next_execution_date))
    def next_dagrun_after_date(self, date_last_automated_dagrun: Optional[pendulum.DateTime]):