Prefer floor rounding for Qt 5.14+ fractional DPI handling

* Non-integer DPI handling is fundamentally a broken concept, because UIs are
  essentially pixel art with some vector drawing. Rounding down half fractions
  seems to be a better tradeoff than rounding up or trying to render them as-is.

qrenderdoc/Code/qrenderdoc.cpp

@@ -94,6 +94,11 @@ int main(int argc, char *argv[])
   QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
   QGuiApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
 
+#if(QT_VERSION >= QT_VERSION_CHECK(5, 14, 0))
+  QGuiApplication::setHighDpiScaleFactorRoundingPolicy(
+      Qt::HighDpiScaleFactorRoundingPolicy::RoundPreferFloor);
+#endif
+
   QApplication::setApplicationVersion(lit(FULL_VERSION_STRING));
 
 // shortcut here so we can run this with a non-GUI application