Document jQuery.event.special.<event>.(preDispatch | postDispatch) methods

See 
- https://github.com/jquery/jquery/blob/0019a463bdcb81dc6ba3434505a45774ca27f363/src/event.js#L374-376
- https://github.com/jquery/jquery/blob/0019a463bdcb81dc6ba3434505a45774ca27f363/src/event.js#L411-413
