Transform BubbleEvent and DirectEvent into DirectEventHandler and BubblingEventHandler

Summary:
It appears that `(e: BubblingEvent<T>) = mixed` exists only in given context and it's pointless to keep in this way. It could be simplified to `BubblingEventHandler<T>` without any negative consequences and that's the motivation of this diff.

The only tradeoff of this decision is leaving an opportunity to declare Bubbling/Direct event in the top of the file bc then analysing the code becomes much more difficult. However, it's not used anywhere so it's not a problem now and probably any time.

Also, changes the names to `DirectEventHandler` and `BubblingEventHandler` which are more related to current state. The names were updated in many places in code.

Reviewed By: rubennorte

Differential Revision: D16054571

fbshipit-source-id: 741d075eb46b80bac8eb73a6b30fc0b448cb3902

Libraries/Components/RefreshControl/AndroidSwipeRefreshLayoutNativeComponent.js

@@ -13,7 +13,7 @@
 import codegenNativeComponent from '../../Utilities/codegenNativeComponent';
 
 import type {
-  DirectEvent,
+  DirectEventHandler,
   Float,
   Int32,
   WithDefault,
@@ -56,7 +56,7 @@ type NativeProps = $ReadOnly<{|
   /**
    * Called when the view starts refreshing.
    */
-  onRefresh?: ?(event: DirectEvent<null>) => mixed,
+  onRefresh?: ?DirectEventHandler<null>,
 
   /**
    * Whether the view should be indicating an active refresh.