[objective-c/en] Couple of inconsistencies

[mkmkme]

I've found a couple of issues in the given code that I can't fix myself due to lack of skill in Objective-C and/or not getting the authors' intention in some particular parts of the code. If anyone gives any hints, I'll be happy to fix this myself.

• [ ] MyClass contains a couple of variables both in declaration and implementation:

  
  @interface MyClass : NSObject
  {
  int count;
  @private id data;
  NSString *name;
  }

@implementation MyClass { long distance; NSNumber *height; }

However, since these are not properties, XCode is getting confused when trying to access them:
<img width="1212" alt="image" src="https://user-images.githubusercontent.com/4062234/146678657-7bebec9e-3d29-4437-85b6-f8af6fc0bc0a.png">

- [ ] The same issue applies to `height` in `@implementation` block:
```objective-c
@implementation MyClass {
    long distance;
    NSNumber *height;
}

XCode is confused and refuses to compile myClassFromHeight:

• [ ] MyProtocol, used for declaring MyClass, is never declared

[mkmkme]

Extension example also confuses XCode quite a bit:

Also, the return type of the overloaded function is also missing the asterisk.