**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
"""
        Set ``is_active=False`` on the DAGs for which the DAG files have been removed.
        Additionally change ``is_active=False`` to ``True`` if the DAG file exists.
        :param alive_dag_filelocs: file paths of alive DAGs
        :param session: ORM Session
        """
        log.debug("Deactivating DAGs (for which DAG files are deleted) from %s table ", cls.__tablename__)
        dag_models = session.query(cls).all()
        try:
            for dag_model in dag_models:
                if dag_model.fileloc is not None:
                    if correct_maybe_zipped(dag_model.fileloc) not in alive_dag_filelocs:
                        dag_model.is_active = False
                    else:
                        
                        
                        if not dag_model.is_active:
                            dag_model.is_active = True
                else:
                    continue
            session.commit()
        except Exception:
            session.rollback()
            raise
    @classmethod
    def dags_needing_dagruns(cls, session: Session):