State triggers: Add a shorthand to only conside "value" state changes

I don’t - all my state triggers have to/from (or both) defined, but I don’t want to derail this thread.

Back on track, this FR might be a duplicate of this, but I’ll leave it up to you to decide whether it is or not.

There is also this related WTH which was resolved by the addition of has_value, though I don’t believe this is exposed in UI.