remote-desktop: Consolidate the "Desktop Sharing" term
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.
I am splitting this off !2182 (merged) because that MR is still incomplete (the certificate handling part).