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

[Fatih Uzunoğlu]

 > They will always come before the xdg_shelll.configure event.

But that defines the latest time, we are interested in the earliest time 
it is sent.

My point is/was that if practically major compositors send the scale 
right after the initial surface commit, we can rely on that behavior and 
do one/two round trips so that we can expose the scale to the 
application possibly in `QWindow::create()`, not waiting for the 
exposure or `xdg_shelll.configure`.

The idea is that one/two round trips would incur negligible waiting 
time, and in turn the application can synchronously use the proper scale.

Of course if the scale depends on which monitor the window is in, it 
means that there may be no way to get that in `QWindow::create()` 
(assuming that can be known only when the window is configured and 
exposed), but in majority of cases where there is one screen or multiple 
screens with same scale, the preferred scale (or fractional scale) may 
be detected early on, provided that the compositor sends it.