New 'isConnected' API

Summary: Expose the newly created `isConnected` API to iOS FlipperClient API.

Reviewed By: antonk52

Differential Revision: D46841190

fbshipit-source-id: c36eb08427d60c73fad8f92100df5d012149b4a8

iOS/FlipperKit/FlipperClient.mm

@@ -182,6 +182,10 @@ using WrapperPlugin = facebook::flipper::FlipperCppWrapperPlugin;
 #endif
 }
 
+- (BOOL)isConnected {
+  return _cppClient->isConnected();
+}
+
 - (NSString*)getState {
   return @(_cppClient->getState().c_str());
 }