Make generated EventEmitter C++ code not cause compiler warnings

Summary:
Changelog: [Internal]

While working on implementing [Event Timing API](https://www.w3.org/TR/event-timing/) I've noticed that there are multiple compiler warnings about unused lambda captures, which are coming from generated C++ code for EventEmitters.

This modifies the codegen so that the corresponding lambda doesn't capture event variable if it's not used in the event handler, thus getting rid of warnings.

Reviewed By: christophpurrer

Differential Revision: D42281899

fbshipit-source-id: 98442bb9f3ce374755188d818a9b2d6a8050bf15

packages/react-native-codegen/e2e/__tests__/components/__snapshots__/GenerateEventEmitterCpp-test.js.snap

@@ -217,14 +217,14 @@ void EventPropsNativeComponentViewEventEmitter::onOrientationChange(OnOrientatio
   });
 }
 void EventPropsNativeComponentViewEventEmitter::onEnd(OnEnd event) const {
-  dispatchEvent(\\"end\\", [event=std::move(event)](jsi::Runtime &runtime) {
+  dispatchEvent(\\"end\\", [](jsi::Runtime &runtime) {
     auto payload = jsi::Object(runtime);
     
     return payload;
   });
 }
 void EventPropsNativeComponentViewEventEmitter::onEventBubblingWithPaperName(OnEventBubblingWithPaperName event) const {
-  dispatchEvent(\\"eventBubblingWithPaperName\\", [event=std::move(event)](jsi::Runtime &runtime) {
+  dispatchEvent(\\"eventBubblingWithPaperName\\", [](jsi::Runtime &runtime) {
     auto payload = jsi::Object(runtime);
     
     return payload;

packages/react-native-codegen/src/generators/components/GenerateEventEmitterCpp.js

@@ -67,14 +67,18 @@ const ComponentTemplate = ({
   structName: string,
   dispatchEventName: string,
   implementation: string,
-}) =>
-  `
+}) => {
+  const capture = implementation.includes('event')
+    ? 'event=std::move(event)'
+    : '';
+  return `
 void ${className}EventEmitter::${eventName}(${structName} event) const {
-  dispatchEvent("${dispatchEventName}", [event=std::move(event)](jsi::Runtime &runtime) {
+  dispatchEvent("${dispatchEventName}", [${capture}](jsi::Runtime &runtime) {
     ${implementation}
   });
 }
 `.trim();
+};
 
 const BasicComponentTemplate = ({
   className,