Support VeraCrypt keyfiles and hidden volumes in GNOME Disks

Once these are supported in udisks (#15045 (closed) and #15046 (closed)), we have to extend the unlock dialog in GNOME Disks to allow the user to choose keyfiles and the hidden container option.

Parent Task: #11684 (closed)

Original created by @segfault on 15047 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information