[stable29] fix(lib): get fileinfo before locking

[skjnldsv]

Fixes #53659

When you try to download files from which at least one has been removed from it's federated source, the lockFiles method will mark the storage as unavailable and lock the file in a stale state preventing any further operations.

By getting the fileInfos before, we are able to set-up the mounts before and removing federated shares (mounts) if they are unavailable.

Since 31, the ajax plugin has been removed and the download path have changed, this is only for 29 and 30.

Here is two json stacktrace that show how it used to behave before this patch and how it is supposed to (if you download the file via remote.php/dav, without the zip plugin)
https://gist.github.com/skjnldsv/c8ae6b701f5467984ce0f552e22c5953

[skjnldsv]

/backport! to stable30

[icewind1991]

This could lead to a race condition if the size of any of the files changes between collecting the fileinfos and the moved lock call. Not sure that the effect would be though

[skjnldsv]

This could lead to a race condition if the size of any of the files changes between collecting the fileinfos and the moved lock call. Not sure that the effect would be though

That's the easier approach I could find that made sense to me.
We could also add some more checks to how we do the file lock I guess, but this is also an old deprecated File class 🤷 🤔