fix readonly + format issues

Runtime/gestures/multidrag.cs

             this.initialPosition = initialPosition;
         }
 
-
         public readonly Offset initialPosition;
 
         readonly VelocityTracker _velocityTracker = new VelocityTracker();
 
         public override void addPointer(PointerDownEvent pEvent) {
             D.assert(this._pointers != null);
-            D.assert(pEvent.pointer != null);
             D.assert(pEvent.position != null);
             D.assert(!this._pointers.ContainsKey(pEvent.pointer));
 
 
         void _handleEvent(PointerEvent pEvent) {
             D.assert(this._pointers != null);
-            D.assert(pEvent.pointer != null);
             D.assert(pEvent.timeStamp != null);
             D.assert(pEvent.position != null);
             D.assert(this._pointers.ContainsKey(pEvent.pointer));

Runtime/widgets/drag_target.cs

     public class Draggable<T> : StatefulWidget {
         public Draggable(
             T data,
-            Widget child,
-            Widget feedback,
+            Widget child = null,
+            Widget feedback = null,
             Axis? axis = null,
             Widget childWhenDragging = null,
             Offset feedbackOffset = null,
 
 
     public class LongPressDraggable<T> : Draggable<T> {
-        readonly bool hapticFeedbackOnStart;
-
-            Widget child,
-            Widget feedback,
+            Key key = null,
+            Widget child = null,
+            Widget feedback = null,
-            Key key = null,
             Widget childWhenDragging = null,
             Offset feedbackOffset = null,
             DragAnchor dragAnchor = DragAnchor.child,
             DragEndCallback onDragEnd = null,
-            VoidCallback onDragCompleted = null,
-            bool hapticFeedbackOnStart = true
+            VoidCallback onDragCompleted = null
         ) : base(
             key: key,
             child: child,
             onDragEnd: onDragEnd,
             onDragCompleted: onDragCompleted
         ) {
-            this.hapticFeedbackOnStart = hapticFeedbackOnStart;
+            
         }
 
         public override GestureRecognizer createRecognizer(GestureMultiDragStartCallback onStart) {
-                    if (result != null && this.hapticFeedbackOnStart) {
-                        //HapticFeedback.selectionClick();
-                    }
-
                     return result;
                 }
             };
 
     public class DraggableDetails {
         public DraggableDetails(
-            Velocity velocity,
-            Offset offset,
-            bool wasAccepted = false
+            bool wasAccepted = false,
+            Velocity velocity = null,
+            Offset offset = null
         ) {
             D.assert(velocity != null);
             D.assert(offset != null);
         }
 
-        public bool wasAccepted;
+        public readonly bool wasAccepted;
-        public Velocity velocity;
+        public readonly Velocity velocity;
-        public Offset offset;
+        public readonly Offset offset;
-            DragTargetBuilder<T> builder,
+            DragTargetBuilder<T> builder = null,
+            D.assert(builder != null);
             this.builder = builder;
             this.onWillAccept = onWillAccept;
             this.onAccept = onAccept;
-        public DragTargetBuilder<T> builder;
+        public readonly DragTargetBuilder<T> builder;
-        public DragTargetWillAccept<T> onWillAccept;
+        public readonly DragTargetWillAccept<T> onWillAccept;
-        public DragTargetAccept<T> onAccept;
+        public readonly DragTargetAccept<T> onAccept;
-        public DragTargetLeave<T> onLeave;
+        public readonly DragTargetLeave<T> onLeave;
 
         public override State createState() {
             return new _DragTargetState<T>();
 
         readonly List<_DragTargetState<T>> _enteredTargets = new List<_DragTargetState<T>>();
 
-        OverlayEntry _entry;
-
-        Offset _lastOffset;
-
+        
+        Offset _lastOffset;
+        
+        OverlayEntry _entry;
 
         public void update(DragUpdateDetails details) {
             this._position += this._restrictAxis(details.delta);