**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
'dag_id=%s, task_id=%s, execution_date=%s, start_date=%s, end_date=%s',
            self.dag_id,
            self.task_id,
            self._date_or_empty('execution_date'),
            self._date_or_empty('start_date'),
            self._date_or_empty('end_date'),
        )
        self.set_duration()
        if not test_mode:
            session.add(Log(self.state, self))
            session.merge(self)
        session.commit()
        if not test_mode:
            self._run_mini_scheduler_on_child_tasks(session)
    @provide_session
    @Sentry.enrich_errors
    def _run_mini_scheduler_on_child_tasks(self, session=None) -> None:
        if conf.getboolean('scheduler', 'schedule_after_task_execution', fallback=True):
            from airflow.models.dagrun import DagRun  
            try:
                
                dag_run = with_row_locks(
                    session.query(DagRun).filter_by(
                        dag_id=self.dag_id,
                        execution_date=self.execution_date,
                    ),
                    session=session,
                ).one()