iOS端添加系统表情

对于UITextField或者UITextView，对于系统表情在发送服务器前做编码处理，示例代码如下：

NSCharacterSet *allowedCharacters = [NSCharacterSet characterSetWithCharactersInString:@"!$&'()*+,-./:;=?@_~%#[]"];
    NSString *inputText = [self.originalTextView.text stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacters];

显示时转码后显示，示例代码如下：

NSCharacterSet *allowedCharacters = [NSCharacterSet characterSetWithCharactersInString:@"!$&'()*+,-./:;=?@_~%#[]"];
NSString *showText = [inputText stringByRemovingPercentEncoding];