Summary:
[Folly] Split Futures exceptions by `Promise` vs `Future`.

* Move `Promise` exceptions into the `Promise` header.
* Move `Future` exceptions into the `Future` header.
* Split `NoState` into `PromiseInvalid` and `FutureInvalid`.
* Remove the newly-empty exceptions header.

Reviewed By: andriigrynenko

Differential Revision: D7966499

fbshipit-source-id: 2dc6d2a941493979ebf47b3e70e5cf6a6fbd33cf