**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
self,
        start_date: datetime,
        num: Optional[int] = None,
        end_date: Optional[datetime] = timezone.utcnow(),
    ) -> List[datetime]:
        if num is not None:
            end_date = None
        return utils_date_range(
            start_date=start_date, end_date=end_date, num=num, delta=self.normalized_schedule_interval
        )
    def is_fixed_time_schedule(self):
        """
        Figures out if the DAG schedule has a fixed time (e.g. 3 AM).
        :return: True if the schedule has a fixed time, False if not.
        """
        now = datetime.now()
        cron = croniter(self.normalized_schedule_interval, now)
        start = cron.get_next(datetime)
        cron_next = cron.get_next(datetime)
        if cron_next.minute == start.minute and cron_next.hour == start.hour:
            return True
        return False
    def following_schedule(self, dttm):