HarmonyOS base64编解码

指南参考链接：https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/js-apis-util-V5#base64helper9

示例参考：

import { util } from '@kit.ArkTS';

let base64 = new util.Base64Helper();
let base64skData = base64.decodeSync("MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCjSASCSzDPoXFq/6V5kXhhdH+gLaalmhZ+FNJZCx8Rr94po93Y85Icww
o2jQvnx8tRX0mof0Sk1GqgqSUHniXOJewu6KHDt8wZTnY8ncB");

let ua = new Uint8Array([64, 0, 9, 0, 4, 8, 255, 0, 0, 0, 8, 0])
let baseua = base64.encodeToStringSync(ua);
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