Add FBPortForwarding source code

Summary:
See FBPortForwarding/README.md for an explanation of what this is.
It's required for the upcoming support for physical iOS devices.

To simplify development of the JS app, We're going to bundle the pre-built PortForwardingMacApp
inside the repo, and inside the electron app (static/PortForwardingMacApp.app).
Adding this source so users can build it from source if they choose to.

Reviewed By: danielbuechele

Differential Revision: D13276022

fbshipit-source-id: 99b18e0412cf443bb4a67eb4846cc780e0014de1

iOS/FlipperKit/FKPortForwarding/FKPortForwardingServer.h

@@ -0,0 +1,17 @@
+/**
+ * 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 <Foundation/Foundation.h>
+
+@interface FKPortForwardingServer : NSObject
+
+- (instancetype)init;
+
+- (void)listenForMultiplexingChannelOnPort:(NSUInteger)port;
+- (void)forwardConnectionsFromPort:(NSUInteger)port;
+- (void)close;
+
+@end