Summary: Add test for ```NSDictionary``` and ```NSMutableDictionary```. ```NSMutableDictionary``` is a subclass of ```NSDictionary```. [Doc] ```NSDictionary``` https://developer.apple.com/documentation/foundation/nsdictionary?language=objc ```NSMutableDictionary``` https://developer.apple.com/documentation/foundation/nsmutabledictionary?language=objc Reviewed By: skcho Differential Revision: D22041942 fbshipit-source-id: d1a1aa781