Implement canDownloadFiles and canManageFilesPermissions fields for dataset user permission

Inspired from this issue/TODO in front-end repo, in Dataset Permissions, it asked about adding canDownloadFiles and canManageFilesPermissions permission fields to js-dataverse. Based on the dataset user permission model in js-dataverse repo, we don't have these two fields yet.

In native API, one endpoint Know If a User Can Download at Least One File from a Dataset Version may be relevant to the canDownloadFiles field.

从 src/datasets/domain/models/DatasetUserPermissions.ts 开始，将现有的数据集用户权限字段与请求的 canDownloadFiles 和 canManageFilesPermissions 字段进行比较。阅读“Know If a User Can Download at Least One File from a Dataset Version”的 native API 文档，以确定它是否能为 canDownloadFiles 提供信息。两个字段都在权限模型中得到表示，并且其数据源已确定，即表示完成。