Background Portal Implementation

[leolost2605]

Problem

Currently the flatpak Background Portal isn't available in elementary as the GTK implementation was removed by default with this release as it depends on gnome-shell. However it is needed for the flatpak versions of e.g. Mail, Calendar and Tasks to request autostart.

Proposal

Implement the background portal from scratch or tweak the GTK version to work without gnome-shell.

Prior Art (Optional)

No response

[Marukesu]

The DesktopIntegration interface in gala need to be finished before we can write a background portal implementation, in special, the get_running_applications method.

[leolost2605]

I'm not sure and not very familiar with DBus but eager to learn :) and using D-Spy I found a GetRunningApplications method at /org/pantheon/gala/DesktopInterface under the interface org.pantheon.gala.DesktopIntegration on the bus org.pantheon.gala and it seems to work for me... except for that it doesn't return apps running without a window which I wouldn't really consider blocking.
Or am I missing something here?
Otherwise I would try and work on implementing the portal :)