**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
"""Clear task instances."""
    body = request.get_json()
    try:
        data = clear_task_instance_form.load(body)
    except ValidationError as err:
        raise BadRequest(detail=str(err.messages))
    dag = current_app.dag_bag.get_dag(dag_id)
    if not dag:
        error_message = f"Dag id {dag_id} not found"
        raise NotFound(error_message)
    reset_dag_runs = data.pop('reset_dag_runs')
    task_instances = dag.clear(get_tis=True, **data)
    if not data["dry_run"]:
        clear_task_instances(
            task_instances,
            session,
            dag=dag,
            activate_dag_runs=False,  
        )
        if reset_dag_runs:
            dag.set_dag_runs_state(