Simplified event registration

Summary:
Our events all follow a common pattern, so there's no good reason why the configuration should be so verbose. This diff eliminates that redundancy, and gives us the freedom to simplify the underlying mechanism in future without further churning the call sites.

React/Views/RCTSwitchManager.m

@@ -30,7 +30,7 @@ RCT_EXPORT_MODULE()
 - (void)onChange:(RCTSwitch *)sender
 {
   if (sender.wasOn != sender.on) {
-    [self.bridge.eventDispatcher sendInputEventWithName:@"topChange" body:@{
+    [self.bridge.eventDispatcher sendInputEventWithName:@"change" body:@{
        @"target": sender.reactTag,
        @"value": @(sender.on)
      }];