Xpra: Ticket #2519: show remote screen size if relevant

It is useful to have for "shadow" and "desktop" servers.

As per mailing list: client side window is too tall and wide, users will miss reporting important information unless we print it.

Thu, 19 Dec 2019 05:43:38 GMT - Antoine Martin: status changed; resolution set

Done in r24765.

Client now prints this when shadowing my main display:

Xpra GTK3 shadow server version 4.0-r24738 64-bit
 running on Linux Fedora 31 ThirtyOne
 remote desktop size is 3840x2160 with 1 screen:
  :1.0 (1016x572 mm - DPI: 96x95) workarea: 3840x2133 at 0x27
    SEK DP-4 (708x398 mm - DPI: 137x137)

Sat, 23 Jan 2021 05:53:29 GMT - migration script:

this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2519