**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
self.log.info(hr_line_break)
        self.log.info("Starting attempt %s of %s", self.try_number, self.max_tries + 1)
        self.log.info(hr_line_break)
        self._try_number += 1
        if not test_mode:
            session.add(Log(State.RUNNING, self))
        self.state = State.RUNNING
        self.end_date = None
        if not test_mode:
            session.merge(self)
        session.commit()
        
        
        settings.engine.dispose()  
        if verbose:
            if mark_success:
                self.log.info("Marking success for %s on %s", self.task, self.execution_date)
            else:
                self.log.info("Executing %s on %s", self.task, self.execution_date)
        return True
    def _date_or_empty(self, attr):
        if hasattr(self, attr):
            date = getattr(self, attr)
            if date:
                return date.strftime('%Y%m%dT%H%M%S')
        return ''
    @provide_session
    @Sentry.enrich_errors
    def _run_raw_task(