remote-desktop: Add "Remote Session" settings

This change will update the UI and internal reference names to use the "Desktop Sharing" term, which refers to sharing a user's screen with remote connections.

This differentiation is being introduced now so that we can avoid conflict with "Remote Session", which will refer to headless/dedicated remote desktop sessions.

Mockups https://gitlab.gnome.org/Teams/Design/settings-mockups/-/raw/master/remote-desktop/remote-desktop.png

See #2827 (closed)