This indicates that starting at this token, the sentence should not be ended until
we see a ForcedSentenceEndAnnotation. Used to force the ssplit annotator
(eg the WordToSentenceProcessor) to keep tokens in the same sentence
until ForcedSentenceEndAnnotation is seen.
Returns the type associated with this annotation. This method must
return the same class type as its value type parameter. It feels like
one should be able to get away without this method, but because Java
erases the generic type signature, that info disappears at runtime.