Requests the isolate to shut down.
The isolate is requested to terminate itself.
The priority argument specifies when this must happen.
The priority, when provided, must be one of immediate or
beforeNextEvent (the default).
The shutdown is performed at different times depending on the priority:
immediate: The isolate shuts down as soon as possible.
Control messages are handled in order, so all previously sent control
events from this isolate will all have been processed.
The shutdown should happen no later than if sent with
beforeNextEvent.
It may happen earlier if the system has a way to shut down cleanly
at an earlier time, even during the execution of another event.beforeNextEvent: The shutdown is scheduled for the next time
control returns to the event loop of the receiving isolate,
after the current event, and any already scheduled control events,
are completed.If terminateCapability is null, or it's not the terminate capability
of the isolate identified by controlPort,
the kill request is ignored by the receiving isolate.
external void kill({int priority: beforeNextEvent});