HarmonyOS promptAction.openCustomDialog圆角无法修改，当前圆角太大了

可使用dialogController的方式实现，参考示例如下：

// Index.ets
@CustomDialog
struct CustomDialogExample {
  controller?: CustomDialogController
  cancel: () => void = () => {
  }
  confirm: () => void = () => {
  }

  build() {
    Column() {
      Text('自定义弹窗')
        .fontSize(30)
        .height(100)
      Button('点我关闭弹窗')
        .onClick(() => {
          if (this.controller != undefined) {
            this.controller.close()
          }
        })
        .margin(20)
    }
  }
}

@Entry
@Component
struct Index {
  dialogController: CustomDialogController | null = new CustomDialogController({
    builder: CustomDialogExample({
      cancel: () => {
        this.onCancel()
      },
      confirm: () => {
        this.onAccept()
      }
    }),
    cancel: this.existApp,
    autoCancel: true,
    alignment: DialogAlignment.Center,
    offset: { dx: 0, dy: -20 },
    gridCount: 2, //设置宽度
    showInSubWindow: false,
    isModal: true,
    customStyle: false,
    cornerRadius: 50, //设置圆角
  })

  // 在自定义组件即将析构销毁时将dialogControlle置空
  aboutToDisappear() {
    this.dialogController = null // 将dialogController置空
  }

  onCancel() {
    console.info('Callback when the first button is clicked')
  }

  onAccept() {
    console.info('Callback when the second button is clicked')
  }

  existApp() {
    console.info('Click the callback in the blank area')
  }

  build() {
    Column() {
      Button('click me')
        .onClick(() => {
          if (this.dialogController != null) {
            this.dialogController.open()
          }
        }).backgroundColor(0x317aff)
    }.width('100%').margin({ top: 5 })
  }
}