Draft: Add Input Capture portal backend
This is a backend for https://github.com/flatpak/xdg-desktop-portal/pull/714.
Needs https://gitlab.gnome.org/jadahl/mutter/-/commits/wip/input-capture.
This is a backend for https://github.com/flatpak/xdg-desktop-portal/pull/714.
Needs https://gitlab.gnome.org/jadahl/mutter/-/commits/wip/input-capture.