**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/api_connexion/endpoints/task_instance_endpoint.py
session=session,
                start_date=data["start_date"],
                end_date=data["end_date"],
                state=State.RUNNING,
            )
    task_instances = task_instances.join(
        DR, and_(DR.dag_id == TI.dag_id, DR.execution_date == TI.execution_date)
    ).add_column(DR.run_id)
    return task_instance_reference_collection_schema.dump(
        TaskInstanceReferenceCollection(task_instances=task_instances.all())
    )
@security.requires_access(
    [
        (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
        (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG_RUN),
        (permissions.ACTION_CAN_EDIT, permissions.RESOURCE_TASK_INSTANCE),
    ]
)
@provide_session
def post_set_task_instances_state(dag_id, session):
    """Set a state of task instances."""
    body = request.get_json()
    try:
        data = set_task_instance_state_form.load(body)
    except ValidationError as err:
        raise BadRequest(detail=str(err.messages))
    error_message = f"Dag ID {dag_id} not found"
    try:
        dag = current_app.dag_bag.get_dag(dag_id)
        if not dag: