**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/taskinstance.py
dag_id: str,  
        task_id: str,
        execution_date: datetime,
        mark_success: bool = False,
        ignore_all_deps: bool = False,
        ignore_depends_on_past: bool = False,
        ignore_task_deps: bool = False,
        ignore_ti_state: bool = False,
        local: bool = False,
        pickle_id: Optional[int] = None,
        file_path: Optional[str] = None,
        raw: bool = False,
        job_id: Optional[str] = None,
        pool: Optional[str] = None,
        cfg_path: Optional[str] = None,
    ) -> List[str]:
        """
        Generates the shell command required to execute this task instance.
        :param dag_id: DAG ID
        :type dag_id: str
        :param task_id: Task ID
        :type task_id: str
        :param execution_date: Execution date for the task
        :type execution_date: datetime