**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
super().__init__(**kwargs)
        if self.concurrency is None:
            self.concurrency = conf.getint('core', 'dag_concurrency')
        if self.has_task_concurrency_limits is None:
            
            self.has_task_concurrency_limits = True
    def __repr__(self):
        return f"<DAG: {self.dag_id}>"
    @property
    def timezone(self):
        return settings.TIMEZONE
    @staticmethod
    @provide_session
    def get_dagmodel(dag_id, session=None):