Let OS handle DPI scaling for now. Should let Qt do the work when it's more mature.

Opt-in to the high DPI pixmap support
Closes #2963.

dist/windows/qt.conf

@@ -1,2 +1,5 @@
 [Paths]
 Translations = translations
+
+[Platforms]
+WindowsArguments = dpiawareness=1

src/app/application.cpp

@@ -92,6 +92,9 @@ Application::Application(const QString &id, int &argc, char **argv)
     setApplicationName("qBittorrent");
     initializeTranslation();
 #ifndef DISABLE_GUI
+#ifdef QBT_USES_QT5
+    setAttribute(Qt::AA_UseHighDpiPixmaps, true);  // opt-in to the high DPI pixmap support
+#endif // QBT_USES_QT5
     setQuitOnLastWindowClosed(false);
 #ifdef Q_OS_WIN
     connect(this, SIGNAL(commitDataRequest(QSessionManager &)), this, SLOT(shutdownCleanup(QSessionManager &)), Qt::DirectConnection);