HarmonyOS 鸿蒙Next 清理app缓存的方法

当前没有清除缓存的接口，推荐下面：

查询缓存用storageStatistics.getCurrentBundleStats()接口。清除文件缓存，需要调用context的cacheDir获取缓存，然后调用系统文件fs接口，判断是文件或者文件夹，再分别消除缓存。 详细用法见下面的链接：

查询：https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/js-apis-file-storage-statistics-V5

import { common } from '[@kit](/user/kit).AbilityKit'
import fs from '[@ohos](/user/ohos).file.fs';
import { BusinessError } from '[@kit](/user/kit).BasicServicesKit';

function clearCache(context:common.UIAbilityContext) {
 let cacheDir = context.cacheDir
 fs.listFile(cacheDir).then((filenames) => {
   for (let i = 0;i < filenames.length; i++) {
     let dirPath = cacheDir + filenames[i] // 判断是否文件夹
     let isDirectory: boolean = false
     try {
       isDirectory = fs.statSync(dirPath).isDirectory()
     } catch (e) {
       console.log(e)
     }
     if (isDirectory) {
       fs.rmdirSync(dirPath)
     } else {
       fs.unlink(dirPath).then(() => {
         console.info('remove file succeed');
       }).catch((err: BusinessError) => {
         console.info("remove file failed with error message: " + err.message + ", error code: " + err.code);
       });
     }
   }
 })
}