Add double tap gesture and fix bugs

Changlog-Added: Image double-tap gesture
Closes: #397

damus/Modifiers/SwipeToDismiss.swift

@@ -11,13 +11,17 @@ struct SwipeToDismissModifier: ViewModifier {
     let minDistance: CGFloat?
     var onDismiss: () -> Void
     @State private var offset: CGSize = .zero
+    @GestureState private var viewOffset: CGSize = .zero
 
     func body(content: Content) -> some View {
         content
-            .offset(y: offset.height)
-            .animation(.interactiveSpring(), value: offset)
+            .offset(y: viewOffset.height)
+            .animation(.interactiveSpring(), value: viewOffset)
             .simultaneousGesture(
                 DragGesture(minimumDistance: minDistance ?? 10)
+                    .updating($viewOffset, body: { value, gestureState, transaction in
+                        gestureState = CGSize(width: value.location.x - value.startLocation.x, height: value.location.y - value.startLocation.y)
+                    })
                     .onChanged { gesture in
                         if gesture.translation.width < 50 {
                             offset = gesture.translation