[ios] add emptyInfo to the TrackRecordingInfo

`emptyInfo` is used as an initial (zero) state during the recoding process starting to notify the info observers
Signed-off-by: Kiryl Kaveryn <kirylkaveryn@gmail.com>

iphone/CoreApi/CoreApi/TrackRecorder/TrackRecordingInfo.h

@@ -11,6 +11,8 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic, readonly) NSString * maxElevation;
 @property (nonatomic, readonly) NSString * minElevation;
 
++ (TrackRecordingInfo *)emptyInfo;
+
 @end
 
 NS_ASSUME_NONNULL_END

iphone/CoreApi/CoreApi/TrackRecorder/TrackRecordingInfo.mm

@@ -5,6 +5,10 @@
 
 @implementation TrackRecordingInfo
 
++ (TrackRecordingInfo *)emptyInfo {
+  return [[TrackRecordingInfo alloc] initWithGpsTrackInfo:GpsTrackInfo()];
+}
+
 @end
 
 @implementation TrackRecordingInfo (Core)