**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
scheduler_lock = Column(Boolean)
    
    pickle_id = Column(Integer)
    
    
    
    
    fileloc = Column(String(2000))
    
    owners = Column(String(2000))
    
    description = Column(Text)
    
    default_view = Column(String(25))
    
    schedule_interval = Column(Interval)
    
    tags = relationship('DagTag', cascade='all,delete-orphan', backref=backref('dag'))
    concurrency = Column(Integer, nullable=False)
    has_task_concurrency_limits = Column(Boolean, nullable=False)
    
    next_dagrun = Column(UtcDateTime)
    
    next_dagrun_create_after = Column(UtcDateTime)
    __table_args__ = (
        Index('idx_root_dag_id', root_dag_id, unique=False),
        Index('idx_next_dagrun_create_after', next_dagrun_create_after, unique=False),
    )
    NUM_DAGS_PER_DAGRUN_QUERY = conf.getint('scheduler', 'max_dagruns_to_create_per_loop', fallback=10)
    def __init__(self, **kwargs):