HarmonyOS 选择文件后通过文件地址获取文件大小报错no such file

可使用fs.statSync(file2.fd)来读取文件fd，参考示例：

import { BusinessError } from '@kit.BasicServicesKit';
import picker from '@ohos.file.picker';
import { common } from '@kit.AbilityKit';
import fs from '@ohos.file.fs';

@Entry
@Component
struct Index {
  @State selectedFileUri: string = ""

  build() {
    Column() {
      Button("选择文件")
        .onClick(() => {
          this.pickFile()
        })
    }
    .justifyContent(FlexAlign.Center)
    .width('100%')
    .height('100%')
  }

  pickFile() {
    try {
      let documentSelectOptions = new picker.DocumentSelectOptions();
      let context = getContext(this) as common.Context;
      let documentPicker = new picker.DocumentViewPicker(context);
      documentPicker.select(documentSelectOptions).then((documentSelectResult: Array<string>) => {
        if (documentSelectResult.length > 0) {
          this.selectedFileUri = documentSelectResult[0]
          // 读取
          let file2 = fs.openSync(this.selectedFileUri, 0o2);
          let stat = fs.statSync(file2.fd);
          let buf2 = new ArrayBuffer(stat.size);
          fs.readSync(file2.fd, buf2); // 以同步方法从流文件读取数据。
          fs.fsyncSync(file2.fd);
          fs.closeSync(file2.fd);
        }
      }).catch((err: BusinessError) => {
        console.error('DocumentViewPicker.select failed with err: ' + JSON.stringify(err));
      });

    } catch (error) {
      let err: BusinessError = error as BusinessError;
      console.error('DocumentViewPicker failed with err: ' + JSON.stringify(err));
    }
  }
}