如何实现拖拽时列表项占位动画的效果
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拖拽Grid时，列表项显示占位动画效果。实现步骤如下：

1.  在Grid组件下设置属性editMode(true)，使Grid进入编辑模式。进入编辑模式后，可以拖拽Grid组件内部的GridItem。
2.  在onItemDragStart回调中设置拖拽时显示的组件。
3.  在onItemDrop中获取拖拽起始位置和拖拽插入位置，并完成数组位置交换逻辑。
    
    @Entry
    @Component
    struct GridExample {
      @State numbers: string\[\] = \[\];
      scroller: Scroller = new Scroller();
      @State text: string = 'drag';
    
      @Builder
      pixelMapBuilder() {
        Column() {
          Text(this.text)
            .fontSize(16)
            .backgroundColor(0xF9CF93)
            .width(80)
            .height(80)
            .textAlign(TextAlign.Center)
        }
      }
    
      aboutToAppear() {
        for (let i = 1; i <= 15; i++) {
          this.numbers.push(i + '');
        }
      }
    
      changeIndex(index1: number, index2: number) {
        _// Swap array positions_
        let temp = this.numbers\[index1\];
        this.numbers\[index1\] = this.numbers\[index2\];
        this.numbers\[index2\] = temp;
      }
    
      build() {
        Column({ space: 5 }) {
          Grid(this.scroller) {
            ForEach(this.numbers, (day: string) => {
              GridItem() {
                Text(day)
                  .fontSize(16)
                  .backgroundColor(0xF9CF93)
                  .width(80)
                  .height(80)
                  .textAlign(TextAlign.Center)
                  .onTouch((event: TouchEvent) => {
                    if (event.type === TouchType.Up) {
                      this.text = day;
                    }
                  })
              }
            })
          }
          .columnsTemplate('1fr 1fr 1fr')
          .columnsGap(10)
          .rowsGap(10)
          .onScrollIndex((first: number) => {
            console.info(first.toString());
          })
          .width('90%')
          .backgroundColor(0xFAEEE0)
          .height(300)
          .editMode(true) _// Set whether the Grid enters editing mode. When entering editing mode, you can drag and drop the GridItem inside the Grid component_
          .onItemDragStart((event: ItemDragInfo, itemIndex: number) => { _// When dragging the component bound to this event for the first time, a callback is triggered._
            return this.pixelMapBuilder(); _//Set the image displayed during the drag and drop process._
          })
         _ // The component bound to this event can be used as a drag and drop release target. When the drag behavior stops within the scope of this component, a callback is triggered._
          .onItemDrop((event: ItemDragInfo, itemIndex: number, insertIndex: number, isSuccess: boolean) => {
            _// Drag the starting position of itemIndex, drag the insertion position of insertIndex_
            this.changeIndex(itemIndex, insertIndex)
          })
        }.width('100%').margin({ top: 5 })
      }
    }