fix(mobile): tall image scrolling (#25649)

Add cross-axis gesture detection in PhotoView so vertical scrolling works on tall images that don't fill the screen width (have black bars)

Author: ByteSizedMarius

mobile/lib/widgets/photo_view/src/core/photo_view_gesture_detector.dart

@@ -203,9 +203,13 @@ class PhotoViewGestureRecognizer extends ScaleGestureRecognizer {
 
   void _decideIfWeAcceptEvent(PointerEvent event) {
     final move = _initialFocalPoint! - _currentFocalPoint!;
-    final bool shouldMove = validateAxis == Axis.vertical
-        ? hitDetector!.shouldMove(move, Axis.vertical)
-        : hitDetector!.shouldMove(move, Axis.horizontal);
+
+    // Accept gesture if movement is possible in the direction the user is swiping
+    final bool isHorizontalGesture = move.dx.abs() > move.dy.abs();
+    final bool shouldMove = isHorizontalGesture
+        ? hitDetector!.shouldMove(move, Axis.horizontal)
+        : hitDetector!.shouldMove(move, Axis.vertical);
+
     if (shouldMove || _pointerLocations.keys.length > 1) {
       final double spanDelta = (_currentSpan! - _initialSpan!).abs();
       final double focalPointDelta = (_currentFocalPoint! - _initialFocalPoint!).distance;