**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
include_downstream=True,
                            )
                            tis = tis.union(
                                downstream.clear(
                                    start_date=tii.execution_date,
                                    end_date=tii.execution_date,
                                    only_failed=only_failed,
                                    only_running=only_running,
                                    confirm_prompt=confirm_prompt,
                                    include_subdags=include_subdags,
                                    include_parentdag=False,
                                    dag_run_state=dag_run_state,
                                    get_tis=True,
                                    session=session,
                                    recursion_depth=recursion_depth + 1,
                                    max_recursion_depth=max_recursion_depth,
                                    dag_bag=dag_bag,
                                    visited_external_tis=visited_external_tis,
                                )
                            )
                        visited_external_tis.add(ti_key)
        if get_tis:
            return tis
        tis = tis.all()
        if dry_run:
            session.expunge_all()
            return tis
        
        
        count = len(tis)