Add back VirtualBox guest support

Removed on devel in !652 (merged) (which should make its way into stable and thus 4.27 via !721 (merged)) in order to fix #18643 (closed), and not solved by #18666 (closed).

The main impact reported by our users is: being unable to change the screen resolution of Tails by resizing the virtual machine window. We documented how to change the screen resolution in !730 (merged).

Edited Mar 24, 2022 by intrigeri

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