Add org.freedesktop.portal.ScreenCast implementaion

[jamzy118]

Hello,

I've recently moved from Plasma to Cinnamon on my Arch and I'm trying to use Valent as a drop-in replacement for KDE Connect. Most of the things work properly, but attempt to remotely control the mouse throws a lot of

on_session_created(): GDBus.Error:org.freedesktop.DBus.Error.InvalidArgs: No such interface “org.freedesktop.portal.ScreenCast”

as far as I see with /usr/lib/xdg-desktop-portal -vr and in the source code, there is no implementation of ScreenCast - any chance we could have this?

GNOME one here

[levivk]

I also see this error with Gnome network displays (https://gitlab.gnome.org/GNOME/gnome-network-displays). I assume the missing ScreenCast interface to be the reason for it not working.
Is there any potential workaround (i.e. another compatible backend)? Or do we need a Cinnamon specific implementation of ScreenCast?

[Magissia]

Coming for the very same reason jamzy118 did, for the exact same usage.
I have a running setup with Android KDE Connect + ArchLinux Valent to test changes if help is needed.

[stephematician]

Just pinging that this would also resolve mate-desktop/mate-desktop#504 .