Port apps to use portals

The idea is to use portals instead create holes in the flatpak sandbox

Documentation:

• NOTE: Toolkits provide support for some portals for free. For example:
  • https://docs.flatpak.org/en/latest/portals-gtk.html
  • https://docs.flatpak.org/en/latest/portals-qt.html
• https://docs.flatpak.org/en/latest/desktop-integration.html#portals
• Portal specifications: https://flatpak.github.io/xdg-desktop-portal/portal-docs.html
• libportal: https://github.com/flatpak/libportal
• Rust bindings: https://github.com/bilelmoussaoui/ashpd
• Blog post explaining how portals work: https://who-t.blogspot.com/2021/08/flatpak-portals-how-do-they-work.html

Relevant repos:

• https://github.com/flatpak/xdg-desktop-portal-gtk/
• https://gitlab.gnome.org/GNOME/xdg-desktop-portal-gnome

Camera portal:

• cheese: cheese#95
• decoder: World/decoder!11 (merged)
• firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1724900

Location portal:

• epiphany: epiphany#1592
• gnome-clocks: gnome-clocks#149 (closed)
• gnome-maps: gnome-maps#307 (closed)
• gnome-weather: gnome-weather#123 (closed)
• gnome-calendar: gnome-calendar!197 (merged)