add support for better drag&drop functionality in Editor

com.unity.uiwidgets/Runtime/editor/editor_window.cs

                         physicalY: evt.mousePosition.y * this._devicePixelRatio
                     );
                 }
-                else if (evt.type == EventType.MouseUp || evt.rawType == EventType.MouseUp) {
+                else if (evt.type == EventType.MouseUp || evt.rawType == EventType.MouseUp ||
+                        evt.type == EventType.DragExited) {
                     pointerData = new PointerData(
                         timeStamp: Timer.timespanSinceStartup,
                         change: PointerChange.up,

com.unity.uiwidgets/Runtime/editor/widgets/unity_object_detector.cs

 
     public delegate void DragFromEditorExitCallback();
 
+    public delegate void DragFromEditorStartCallback();
+
+    public delegate void DragFromEditorCancelCallback();
+
+
     public delegate void DragFromEditorReleaseCallback(DragFromEditorDetails details);
 
     public class DragFromEditorDetails {
             DragFromEditorHoverCallback onHover = null,
             DragFromEditorExitCallback onExit = null,
             DragFromEditorReleaseCallback onRelease = null,
+            DragFromEditorStartCallback onStart = null,
+            DragFromEditorCancelCallback onCancel = null,
             HitTestBehavior? behavior = null
         ) : base(key: key) {
             this.child = child;
             this.onDragFromEditorRelease = onRelease;
+            this.onDragFromEditorStart = onStart;
+            this.onDragFromEditorCancel = onCancel;
             this.behavior = behavior;
         }
 
         public readonly DragFromEditorHoverCallback onDragFromEditorHover;
         public readonly DragFromEditorExitCallback onDragFromEditorExit;
         public readonly DragFromEditorReleaseCallback onDragFromEditorRelease;
+        public readonly DragFromEditorStartCallback onDragFromEditorStart;
+        public readonly DragFromEditorCancelCallback onDragFromEditorCancel;
 
         public readonly HitTestBehavior? behavior;
 
         public override Widget build(BuildContext context) {
             Widget result = new Listener(
                 child: this.widget.child,
+                onPointerDown: (evt) => {
+                    this.widget.onDragFromEditorStart?.Invoke();
+                    },
+                onPointerUp: (evt) => {
+                    this.widget.onDragFromEditorCancel?.Invoke();
+                    },
+                onPointerCancel: (evt) => {
+                    this.widget.onDragFromEditorCancel?.Invoke();
+                    },
                 onPointerDragFromEditorEnter: this.widget.onDragFromEditorEnter == null
                     ? ((PointerDragFromEditorEnterEventListener) null)
                     : (evt) => { this.widget.onDragFromEditorEnter.Invoke(); },

com.unity.uiwidgets/Runtime/gestures/converter.cs

 #if UNITY_EDITOR
                     case PointerChange.dragFromEditorMove: {
                         _PointerState state = _ensureStateForPointer(datum, position);
-                        state.startNewPointer();
+                        //state.startNewPointer();
                         yield return new PointerDragFromEditorHoverEvent(
                             timeStamp: timeStamp,
                             pointer: state.pointer,
                         break;
                     case PointerChange.dragFromEditorRelease: {
                         _PointerState state = _ensureStateForPointer(datum, position);
-                        state.startNewPointer();
+                        //state.startNewPointer();
                         yield return new PointerDragFromEditorReleaseEvent(
                             timeStamp: timeStamp,
                             pointer: state.pointer,