HarmonyOS 鸿蒙Next数据迁移的demo有吗

楼主您好，EntryBackupExtAbility.ets 实现可参考：

```typescript
import BackupExtensionAbility, { BundleVersion } from '[@ohos](/user/ohos).application.BackupExtensionAbility';

import { contextConstant } from '[@kit](/user/kit).AbilityKit';

import { fileIo } from '[@kit](/user/kit).CoreFileKit';

const TAG = `BackupExtensionAbility`;

export default class BackupExtension extends BackupExtensionAbility {
  onBackup() {
    console.log(TAG, `onBackup ok`);
  }

  // onRestore 接口是同步接口，其内部所有的异步操作请进行同步等待。
  async onRestore(bundleVersion: BundleVersion): Promise<void> {
    console.log(TAG, `onRestore ok ${JSON.stringify(bundleVersion)}`);

    if (bundleVersion.name.startsWith("0.0.0.0")) {
      // 在此处实现终端设备从HarmonyOS 4.0升级到HarmonyOS NEXT后，应用数据的转换和迁移
      // 涉及异步操作请进行同步等待
      this.context.area = contextConstant.AreaMode.EL2;
      let ceSourcePath = this.context.backupDir + "restore/{APK包名}/ce/"
      let destEl2Path = this.context.filesDir;

      try {
        fileIo.copyDirSync(ceSourcePath, destEl2Path, 1)
        console.log(TAG, `copyEl2Dirsuccess`);
      } catch (error) {
        console.log(TAG, `copyEl2Dirfail`);
      }

      console.log(TAG, `HarmonyOS to HarmonyOS NEXT scenario`);
    } else {
      // 在此处实现从HarmonyOS NEXT设备迁移到HarmonyOS NEXT设备后，应用数据的处理。无特殊要求，可以空实现
      // 涉及异步操作请进行同步等待
      console.log(TAG, `Other scenario`);
    }
  }
}