Add annotations and casts to fix future flow error (facebook#48219)

Summary:
Pull Request resolved: facebook#48219

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D67099060

fbshipit-source-id: fbb975d6194b071aa8f30dcd2b8f7f40130d31fb

packages/rn-tester/js/examples/Experimental/PlatformTest/RNTesterPlatformTestEventRecorder.js

@@ -119,15 +119,14 @@ class RNTesterPlatformTestEventRecorder {
               callback && callback(event, eventType, targetName),
           );
         const eventListenerProps = this.relevantEvents.reduce(
-          (acc, eventName) => {
+          (acc: ViewProps, eventName) => {
             const eventPropName =
               'on' + eventName[0].toUpperCase() + eventName.slice(1);
             return {
               ...acc,
-              // $FlowFixMe[missing-local-annot]
-              [eventPropName]: e => {
+              [eventPropName]: (e => {
                 recordedEventHandler(e, eventName);
-              },
+              }) as $FlowFixMe,
             };
           },
           {},