HarmonyOS Navigation中的title怎么通过CustomBuilder自定义标题呢

可以参考下面的demo来自定义标题：

import { NavRouterDemo } from './NavRouterDemo';

@Entry
@Component
struct Index {
  @State message: string = 'Hello World';
  @Provide('pageInfos') pageInfos: NavPathStack = new NavPathStack()
  @Builder
  PageMap(name: string) {
    if (name === "NavRouterDemo") {
      NavRouterDemo()
    }
  }
  @Builder
  title(){
    Image($r('app.media.startIcon'))
      .width('50vp')
  }

  build() {
    Navigation(this.pageInfos){
      RelativeContainer() {
        Text(this.message)
          .id('HelloWorld')
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
          .alignRules({
            center: { anchor: '__container__', align: VerticalAlign.Center },
            middle: { anchor: '__container__', align: HorizontalAlign.Center }
          })
          .onClick(() => {
            this.pageInfos.pushPathByName('NavRouterDemo',null)
          })
      }
      .height('100%')
      .width('100%')
    }
    .navDestination(this.PageMap)
    .title(this.title())
  }
}
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