成员的完整列表，这些成员属于 NIMQChatAttachmentUploadParam,包括所有继承而来的类成员

cb	NIMQChatAttachmentUploadParam
file_path	NIMQChatAttachmentUploadParam
progress_cb	NIMQChatAttachmentUploadParam
task_id	NIMQChatAttachmentUploadParam
user_data	NIMQChatAttachmentUploadParam