[Development] Wayland: getting a screen's fractional scale before the first window exists

[Fatih Uzunoğlu]

Hello,

Regarding:

 > until the surface is configured by the compositor

I am not sure if the protocol guarantees when 
`wl_surface::preferred_buffer_scale` is sent (or 
`wp_fractional_scale_v1::preferred_scale` in fractional scale case), but 
if in practice major compositors send the scale within one or two event 
loop cycles, then for the sake of application's convenience maybe 
`QWindow::create()` may do one or two arbitrary `wl_display_roundtrip()` 
after the initial commit just to expect the compositor to send the scale.

The waiting time here would probably be negligible, and in turn the 
application can immediately use the proper scale since the roundtrip 
call is blocking, provided that the compositor sent it.