As of version 1.17, xdg-desktop-portal requires desktops to declare
which portals should be used. For Sway, this requires a file
/usr/share/xdg-desktop-portal/sway-portals.conf (or a local user
config).
A reasonable default is to use GTK for the file picker (as wlr doesn't
have file picker support) and wlr for screencast/screenshot support.
Fedora does this similarly. [1]
Upstream is not interested in shipping a configuration file [2] so we
need to do it downstream.
Integrates commits c85a455e and 2f9c63b0 from extra/sway.
Copied from c85a455e: