**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
unixname = Column(String(1000))
    job_id = Column(Integer)
    pool = Column(String(256), nullable=False)
    pool_slots = Column(Integer, default=1, nullable=False)
    queue = Column(String(256))
    priority_weight = Column(Integer)
    operator = Column(String(1000))
    queued_dttm = Column(UtcDateTime)
    queued_by_job_id = Column(Integer)
    pid = Column(Integer)
    executor_config = Column(PickleType(pickler=dill))
    external_executor_id = Column(String(ID_LEN, **COLLATION_ARGS))
    
    
    __table_args__ = (
        Index('ti_dag_state', dag_id, state),
        Index('ti_dag_date', dag_id, execution_date),
        Index('ti_state', state),
        Index('ti_state_lkp', dag_id, task_id, execution_date, state),
        Index('ti_pool', pool, state, priority_weight),
        Index('ti_job_id', job_id),
    )
    dag_model = relationship(
        "DagModel",
        primaryjoin="TaskInstance.dag_id == DagModel.dag_id",
        foreign_keys=dag_id,
        uselist=False,
        innerjoin=True,
    )
    def __init__(self, task, execution_date: datetime, state: Optional[str] = None):