Add Termination.throwIfRequested method, to simplify handling of cooperative termination

From !1071 (comment 2827474):

We discussed the exception, and opted to put it in common.java. We can reuse it for termination checking in general, in some later issue. It would prevent having to pass null everywhere, check for null everywhere. We could just check for termination and let that throw the exception. We then handle that exception in the application framework, automatically.

We can thus use the TerminationException that is added in !1071 (merged).