[Platform] Mark MTRDeviceController as not running before we shut down the cpp commissioner

[bzbarsky-apple]

Reproduction steps

Right now in MTRDeviceConroller shutdown we do the cpp commissioner shutdown and then mark ourselves as "not running". If commissioner shutdown leads to callbacks (which it can, as things get notified as timed out), a caller could try to make calls on us that we would forward on to the Matter stack while it's in a not-very-consistent state.

Platform

darwin

Platform Version(s)

No response

Type

Manually tested with SDK

(Optional) If manually tested please explain why this is only manually tested

Found by code inspection.

Anything else?

No response