**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
return qry.scalar()
    @classmethod
    def get_serialized_fields(cls):
        """Stringified DAGs and operators contain exactly these fields."""
        if not cls.__serialized_fields:
            cls.__serialized_fields = frozenset(vars(DAG(dag_id='test')).keys()) - {
                'parent_dag',
                '_old_context_manager_dags',
                'safe_dag_id',
                'last_loaded',
                '_full_filepath',
                'user_defined_filters',
                'user_defined_macros',
                'partial',
                '_pickle_id',
                '_log',
                'is_subdag',
                'task_dict',
                'template_searchpath',
                'sla_miss_callback',
                'on_success_callback',
                'on_failure_callback',
                'template_undefined',
                'jinja_environment_kwargs',
                
                'has_on_success_callback',
                'has_on_failure_callback',
            }
        return cls.__serialized_fields
    def get_edge_info(self, upstream_task_id: str, downstream_task_id: str) -> EdgeInfoType: