HarmonyOS鸿蒙Next中onDragStart拖拽疑问

列表拖拽排序可使用组合手势`LongPressGesture`长按和`PanGesture`拖动手势事件来实现。
1. 此方法默认无缩放效果
2. 可以控制方向，设置`PanGesture`的direction参数；参考文档：`https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/ts-basic-gestures-pangesture-V5`
3. 参考demo：
```javascript
import curves from '[@ohos](/user/ohos).curves';
import Curves from '[@ohos](/user/ohos).curves'
[@Entry](/user/Entry)
[@Component](/user/Component)
struct ListItemExample {
  [@State](/user/State) private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  [@State](/user/State) dragItem: number = -1
  [@State](/user/State) scaleItem: number = -1
  [@State](/user/State) neighborItem: number = -1
  [@State](/user/State) neighborScale: number = -1
  private dragRefOffset: number = 0
  [@State](/user/State) offsetX: number = 0
  [@State](/user/State) offsetY: number = 0
  private ITEM_INTV: number = 120
  itemMove(index: number, newIndex: number): void {
    let tmp = this.arr.splice(index, 1)
    this.arr.splice(newIndex, 0, tmp[0])
  }
  build() {
    Stack() {
      List({ space: 20, initialIndex: 0 }) {
        ForEach(this.arr, (item: number) => {
          ListItem() {
            Text('' + item)
              .width('50%')
              .height(100)
              .fontSize(16)
              .textAlign(TextAlign.Center)
              .borderRadius(10)
              .backgroundColor(0xFFFFFF)
              .shadow(this.scaleItem == item ? { radius: 70, color: '#15000000', offsetX: 0, offsetY: 0 } :
                { radius: 0, color: '#15000000', offsetX: 0, offsetY: 0 })
              .animation({ curve: Curve.Sharp, duration: 300 })
          }
          .margin({ left: 12, right: 12 })
          .zIndex(this.dragItem == item ? 1 : 0)
          .translate(this.dragItem == item ? { y: this.offsetY } : { y: 0 })
          .gesture(
            // 以下组合手势为顺序识别，当长按手势事件未正常触发时则不会触发拖动手势事件
            GestureGroup(GestureMode.Sequence,
              LongPressGesture({ repeat: true })
                .onAction((event?: GestureEvent) => {
                  animateTo({ curve: Curve.Friction, duration: 300 }, () => {
                    this.scaleItem = item
                  })
                })
                .onActionEnd(() => {
                  animateTo({ curve: Curve.Friction, duration: 300 }, () => {
                    this.scaleItem = -1
                  })
                }),
              PanGesture({ fingers: 1, direction: null, distance: 0 })
                .onActionStart(() => {
                  this.dragItem = item
                  this.dragRefOffset = 0
                })
                .onActionUpdate((event: GestureEvent) => {
                  this.offsetY = event.offsetY - this.dragRefOffset
                  this.neighborItem = -1
                  let index = this.arr.indexOf(item)
                  let curveValue = Curves.initCurve(Curve.Sharp)
                  let value: number = 0
                  //根据位移交换排序
                  if (this.offsetY > this.ITEM_INTV / 2) {
                    animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
                      this.offsetY -= this.ITEM_INTV
                      this.dragRefOffset += this.ITEM_INTV
                      this.itemMove(index, index + 1)
                    })
                  } else if (this.offsetY < -this.ITEM_INTV / 2) {
                    animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
                      this.offsetY += this.ITEM_INTV
                      this.dragRefOffset -= this.ITEM_INTV
                      this.itemMove(index, index - 1)
                    })
                  }
                })
                .onActionEnd((event: GestureEvent) => {
                  animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
                    this.dragItem = -1
                    this.neighborItem = -1
                  })
                  animateTo({
                    curve: curves.interpolatingSpring(14, 1, 170, 17), delay: 150
                  }, () => {
                    this.scaleItem = -1
                  })
                })
            )
              .onCancel(() => {
                animateTo({ curve: curves.interpolatingSpring(0, 1, 400, 38) }, () => {
                  this.dragItem = -1
                  this.neighborItem = -1
                })
                animateTo({
                  curve: curves.interpolatingSpring(14, 1, 170, 17), delay: 150
                }, () => {
                  this.scaleItem = -1
                })
              })
          )
        }, (item: number) => item.toString())
      }
    }.width('100%').height('100%').backgroundColor(0xDCDCDC).padding({ top: 5 })
  }
}