**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.

tests/sensors/test_external_task_sensor.py
"""
    Assert state of task_instances equals the given state.
    """
    task_instance.refresh_from_db()
    assert task_instance.state == state
def clear_tasks(dag_bag, dag, task, start_date=DEFAULT_DATE, end_date=DEFAULT_DATE):
    """
    Clear the task and its downstream tasks recursively for the dag in the given dagbag.
    """
    subdag = dag.sub_dag(task_ids_or_regex=f"^{task.task_id}$", include_downstream=True)
    subdag.clear(start_date=start_date, end_date=end_date, dag_bag=dag_bag)
def test_external_task_marker_transitive(dag_bag_ext):
    """
    Test clearing tasks across DAGs.
    """
    tis = run_tasks(dag_bag_ext)
    dag_0 = dag_bag_ext.get_dag("dag_0")
    task_a_0 = dag_0.get_task("task_a_0")
    clear_tasks(dag_bag_ext, dag_0, task_a_0)
    ti_a_0 = tis["task_a_0"]
    ti_b_3 = tis["task_b_3"]
    assert_ti_state_equal(ti_a_0, State.NONE)
    assert_ti_state_equal(ti_b_3, State.NONE)
def test_external_task_marker_future(dag_bag_ext):