**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
result.task_id: XCom.deserialize_value(result)
                for result in query.with_entities(XCom.task_id, XCom.value)
            }
            values_ordered_by_id = [vals_kv.get(task_id) for task_id in task_ids]
            return values_ordered_by_id
        else:
            xcom = query.with_entities(XCom.value).first()
            if xcom:
                return XCom.deserialize_value(xcom)
    @provide_session
    def get_num_running_task_instances(self, session):
        """Return Number of running TIs from the DB"""
        
        return (
            session.query(func.count())
            .filter(
                TaskInstance.dag_id == self.dag_id,
                TaskInstance.task_id == self.task_id,
                TaskInstance.state == State.RUNNING,
            )
            .scalar()
        )
    def init_run_context(self, raw=False):
        """Sets the log context."""
        self.raw = raw
        self._set_context(self)
    @staticmethod
    def filter_for_tis(tis: Iterable[Union["TaskInstance", TaskInstanceKey]]) -> Optional[BooleanClauseList]:
        """Returns SQLAlchemy filter to query selected task instances"""
        if not tis: