HarmonyOS 弹窗中如何拦截返回键

参考示例：

@Entry
@Component
struct CustomDialogUser1 {
  dialogController: CustomDialogController = new CustomDialogController({
    builder: CustomDialogExample(),
    autoCancel: false,
    onWillDismiss: (dismissDialogAction: DismissDialogAction) => {
      console.info("reason=" + JSON.stringify(dismissDialogAction.reason))
      console.log("dialog onWillDismiss")
      if (dismissDialogAction.reason == DismissReason.TOUCH_OUTSIDE) {
        dismissDialogAction.dismiss()
      }
    },

  })

  onBackPress(): boolean | void {
    return true
  }

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

@CustomDialog
struct CustomDialogExample {
  controller: CustomDialogController = new CustomDialogController({
    builder: CustomDialogExample({}),

  })

  build() {
    Column() {
      Text('我是内容')
        .fontSize(20)
        .margin({ top: 10, bottom: 10 })
    }
  }
}