Fix for the font of truncated sidebar items (#5714). (#5777)

* Fix for the font of truncated sidebar items (#5714).

For windows platforms, retrieve the system font and set it for the FileBrowserTreeWidget. This makes sure that truncated items will use the font as non-truncated items.

* Add TODO to remove the fix when all builds use a recent enough version of qt.

* Add check on QT version and conditionally include the fix.

include/GuiApplication.h

@@ -28,6 +28,7 @@
 #include <QtCore/QObject>
 
 #include "lmms_export.h"
+#include "lmmsconfig.h"
 
 class QLabel;
 
@@ -48,6 +49,9 @@ public:
 	~GuiApplication();
 
 	static GuiApplication* instance();
+#ifdef LMMS_BUILD_WIN32
+	static QFont getWin32SystemFont();
+#endif
 
 	MainWindow* mainWindow() { return m_mainWindow; }
 	FxMixerView* fxMixerView() { return m_fxMixerView; }