**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
"""
        Returns whether or not all the conditions are met for this task instance to be run
        given the context for the dependencies (e.g. a task instance being force run from
        the UI will ignore some dependencies).
        :param dep_context: The execution context that determines the dependencies that
            should be evaluated.
        :type dep_context: DepContext
        :param session: database session
        :type session: sqlalchemy.orm.session.Session
        :param verbose: whether log details on failed dependencies on
            info or debug log level
        :type verbose: bool
        """
        dep_context = dep_context or DepContext()
        failed = False
        verbose_aware_logger = self.log.info if verbose else self.log.debug
        for dep_status in self.get_failed_dep_statuses(dep_context=dep_context, session=session):
            failed = True
            verbose_aware_logger(
                "Dependencies not met for %s, dependency '%s' FAILED: %s",
                self,
                dep_status.dep_name,
                dep_status.reason,
            )
        if failed:
            return False
        verbose_aware_logger("Dependencies all met for %s", self)
        return True
    @provide_session
    def get_failed_dep_statuses(self, dep_context=None, session=None):