HarmonyOS 本地文件如何转为byte数组

请参考链接：

https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/app-file-access-V5#以流的形式读写文件

arraybuffer转Uint8Array请参考：

let arrayBuffer = new ArrayBuffer(100)
buffer.from(arrayBuffer).fill(1)
let arrayBuffer1 = arrayBuffer.slice(0,5)
buffer.from(arrayBuffer).fill(2)
console.log("treeli:::testBuffer =" + new Uint8Array(arrayBuffer))
console.log("treeli:::testBuffer =" + new Uint8Array(arrayBuffer1))
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