[PrintAsObjC] Fix class properties with generic parameters. (#3092)
public static var myDictionary: [String: AnyObject]
becomes
    SWIFT_CLASS_PROPERTY(@property (nonatomic, class, readonly, copy)
      NSDictionary<NSString *, id> * _Nonnull myDictionary;)
and the commas in the ObjC generic break the macro, just like they do with
C++ templates. Fix this by making the macro variadic.
rdar://problem/26879147
(cherry picked from commit a679aca7c52265fe42ca929482a87ac709a830ff)