Implement react-native-flipper on iOS (#795)

Summary:
Implement the react-native-flipper native module on iOS. Uses very similar abstractions as on Android.

## Changelog

[react-native-flipper] Support iOS
Pull Request resolved: https://github.com/facebook/flipper/pull/795

Test Plan:
Tested using the RN TicTacToe example app

{F228406333}

Reviewed By: mweststrate

Differential Revision: D19853017

Pulled By: priteshrnandgaonkar

fbshipit-source-id: d93d35ff984b9ba75f812c4c8e3c82e4d550f0c0

react-native/react-native-flipper/ios/FlipperReactNativeJavaScriptPlugin.h

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <FlipperKit/FlipperPlugin.h>
+#import <FlipperKit/FlipperConnection.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+@class FlipperModule;
+
+@interface FlipperReactNativeJavaScriptPlugin : NSObject<FlipperPlugin>
+
+@property (nonatomic, weak) FlipperModule *module;
+@property (nonatomic, strong, readonly) id<FlipperConnection> connection;
+
+- (instancetype)initWithFlipperModule:(FlipperModule *)module
+                             pluginId:(NSString *)pluginId
+                         inBackground:(BOOL)inBackground;
+
+- (BOOL)isConnected;
+
+- (void)fireOnConnect;
+
+@end
+
+NS_ASSUME_NONNULL_END