When sending a signal to a notification object that has a bound thread that is
in the 'runningVM' start we, ordinarily, want to deliver it by switching back
to the native execution of that thread and delivering the message. If the thread
is in the 'runningVM' state on a different core, then we must not modify its
thread state. Previously we would modify the thread state (changing it to
Running) and then attemptSwitchTo. Switching would fail, as its affinity would
be for a different core, resulting in us enqueing the thread into the
scheduling queue, despite the thread also presently running.
This commit both adds a check to prevent us manipulating a thread that
is actively running on a different core, as well as a remote operation
to tell that core that if it is running a VM it should recheck its
endpoint for a message.
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