**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
self.var = None
            def __getattr__(
                self,
                item: str,
            ):
                self.var = Variable.get(item, deserialize_json=True)
                return self.var
            def __repr__(self):
                return str(self.var)
            @staticmethod
            def get(
                item: str,
                
                default_var: Any = Variable._Variable__NO_DEFAULT_SENTINEL,  
            ):
                """Get Airflow Variable after deserializing JSON value"""
                return Variable.get(item, default_var=default_var, deserialize_json=True)
        return {
            'conf': conf,
            'dag': task.dag,
            'dag_run': dag_run,
            'ds': ds,
            'ds_nodash': ds_nodash,
            'execution_date': pendulum.instance(self.execution_date),
            'inlets': task.inlets,
            'macros': macros,
            'next_ds': next_ds,
            'next_ds_nodash': next_ds_nodash,
            'next_execution_date': next_execution_date,