Because of the Google Drive StorageFile now contains yet another field,
`id`. For other storages `id` == `path`, and thus all common Requests
(such as SavesSyncRequest, DownloadFolderRequest, etc) must be using
id() instead of path(). That way these Requests won't cause id resolving
which could be quite slow (when you call it for all files in the folder,
for example).
GoogleDriveResolveIdRequest gets a lowercase path and searches for the
specified file's id. To do that it lists path's subdirectories one by
one with GoogleDriveListDirectoryByIdRequest.
GoogleDriveListDirectoryByIdRequest gets a Google Drive id and lists
that directory (not recursively).
