Iteration 1: Upstream unlocking VeraCrypt partitions in GVfs

The freeze for GNOME 3.30 is on July 30 so this work must be submitted upstream early enough to ensure it’s merged by then.

The code lives in:

https://gitlab.gnome.org/segfault3/gvfs/tree/support-tcrypt
https://gitlab.gnome.org/segfault3/gvfs/tree/support-file-containers (that’s iteration 2 material done on #15073 (closed) but presumably it can be upstreamed at the same time)

Merge requests:
https://gitlab.gnome.org/GNOME/glib/merge_requests/120 (merged)
https://gitlab.gnome.org/GNOME/gvfs/merge_requests/4 (merged)
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/126 (merged)
https://gitlab.gnome.org/GNOME/gvfs/merge_requests/8 (merged)

Parent Task: #15214 (closed)

Related issues

Related to #15073 (closed)
Blocked by #15218 (closed)

Original created by @segfault on 15222 (Redmine)

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