ui/gtk: Consider scaling when propagating ui info

ui/gtk: Consider scaling when propagating ui info

The ui width and height sent to guest is supposed to be in buffer
coordinate. Hence conversion is required.

If scaling (global window scale and zooming scale) is not respected in
non-free-scale mode, window size could keep changing because of the
existence of the iteration of the following steps:

1. In resize event or configure event, a size larger (or smaller) than
   the currently used one might be calculated due to not considering
   scaling.
2. On reception of the display size change event in guest, the guest
   might decide to do a mode setting and use the larger (or smaller)
   mode.
3. When the new guest scan-out command arrives, QEMU would request the
   window size to change to fit the new buffer size. This will trigger a
   resize event or a configure event, making us go back to step 1.

Signed-off-by: Weifeng Liu <weifeng.liu.z@gmail.com>
Message-ID: <20250511073337.876650-8-weifeng.liu.z@gmail.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Marc-André Lureau <marcandre.lureau@redhat.com>