**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
)
            all_tis.extend(tis)
        if dry_run:
            return all_tis
        count = len(all_tis)
        do_it = True
        if count == 0:
            print("Nothing to clear.")
            return 0
        if confirm_prompt:
            ti_list = "\n".join(str(t) for t in all_tis)
            question = f"You are about to delete these {count} tasks:\n{ti_list}\n\nAre you sure? (yes/no): "
            do_it = utils.helpers.ask_yesno(question)
        if do_it:
            for dag in dags:
                dag.clear(
                    start_date=start_date,
                    end_date=end_date,
                    only_failed=only_failed,
                    only_running=only_running,
                    confirm_prompt=False,
                    include_subdags=include_subdags,
                    dag_run_state=dag_run_state,
                    dry_run=False,
                )
        else:
            count = 0
            print("Cancelled, nothing was cleared.")
        return count
    def __deepcopy__(self, memo):