HarmonyOS 全屏播放video，使用backPress的时候怎么控制只退出全屏而不是web的退出页面

示例参考如下：

import { webview } from '@kit.ArkWeb';
import { faceDetector } from '@kit.CoreVisionKit';

@Entry
@Component
struct WebComponent {
  controller: webview.WebviewController = new webview.WebviewController();
  handler: FullScreenExitHandler | null = null;
  @State backState: boolean = false
  build() {
    Column() {
      Web({ src: 'www.huawei.com', controller: this.controller })
        .onFullScreenEnter((event) => {
          console.log("onFullScreenEnter...")
          this.backState = true
          this.handler = event.handler;
        })
    }
  }

  onBackPress(): boolean | void {
    if (this.handler) {
      this.handler.exitFullScreen();
    }
    return this.backState
  }
}