Implement screencast session restore

[GeorgesStavracas]

Recently xdg-desktop-portal gained the screencast session restore feature, but it requires frontends to implement that. So xdg-desktop-portal-wlr would need to send restore_data back to xdg-desktop-portal when a permission mode is passed.

There is a reference implementation in xdg-desktop-portal-gnome that is merged already: https://gitlab.gnome.org/GNOME/xdg-desktop-portal-gnome/-/merge_requests/14

You can use libportal's mainline branch to test this feature, since it's landed support for it too.

[columbarius]

Thanks for the info. Interested to implement it but it is blocked by #169.

Note:
If screencast without user interaction is required this can be achieved by using the following options.

chooser_type=none
output_name=<Name of output>