iv: Use screen pixel ratio to render sharp text in pixel view tool (#4768)

Improve sharpness of text in pixel view tool for HiDPI screen

Before:
![Screenshot 2025-05-17 at 4 45
50 pm](https://github.com/user-attachments/assets/f2b14aa6-dcbe-46a7-a2d5-a83097baa94d)

After:
![Screenshot 2025-05-17 at 4 47
11 pm](https://github.com/user-attachments/assets/be42f794-d6e0-4b9f-8847-da733b3a3872)


Signed-off-by: Aleksandr Motsjonov <soswow@gmail.com>

Author: soswow

src/iv/ivgl.cpp

@@ -690,7 +690,9 @@ IvGL::shadowed_text(float x, float y, float /*z*/, const std::string& s,
      * Paint on intermediate QImage, AA text on QOpenGLWidget based
      * QPaintDevice requires MSAA
      */
-    QImage t(size(), QImage::Format_ARGB32_Premultiplied);
+    qreal dpr = devicePixelRatio();
+    QImage t(size() * dpr, QImage::Format_ARGB32_Premultiplied);
+    t.setDevicePixelRatio(dpr);
     t.fill(qRgba(0, 0, 0, 0));
     {
         QPainter painter(&t);