**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
"""Returns a tuple that identifies the task instance uniquely"""
        return TaskInstanceKey(self.dag_id, self.task_id, self.execution_date, self.try_number)
    @provide_session
    def set_state(self, state: str, session=None):
        """
        Set TaskInstance state.
        :param state: State to set for the TI
        :type state: str
        :param session: SQLAlchemy ORM Session
        :type session: Session
        """
        current_time = timezone.utcnow()
        self.log.debug("Setting task state for %s to %s", self, state)
        self.state = state
        self.start_date = self.start_date or current_time
        if self.state in State.finished or self.state == State.UP_FOR_RETRY:
            self.end_date = self.end_date or current_time
            self.duration = (self.end_date - self.start_date).total_seconds()
        session.merge(self)
    @property
    def is_premature(self):