patch 9.2.0505: GTK4: text looks blurry on HiDPI displays

patch 9.2.0505: GTK4: text looks blurry on HiDPI displays

Problem:  GTK4: text looks blurry on HiDPI displays
          (Foxe Chen, after v9.2.0501)
Solution: Allocate the cairo surface at physical resolution and set the
          device scale, recreate it on scale-factor changes
          (Yasuhiro Matsumoto).

The backing cairo image surface was created at logical pixel size, so
GTK4 upscaled it when blitting to the physical framebuffer. Allocate
the surface at width*scale x height*scale and apply
cairo_surface_set_device_scale() so drawing code keeps using logical
coordinates while the surface itself has full physical resolution.
Also recreate the surface on notify::scale-factor when the window
moves between monitors with different scales.

fixes:  #20252
closes: #20258

Co-authored-by: Claude <noreply@anthropic.com>
Signed-off-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>