Force Qt to use GLES if desktop GL is not available

Some platforms like the VisionFive 2 don't have working desktop GL,
so they must use GLES to be able to render at all. Qt doesn't try
to fall back if it fails to find a compatible EGL config, so we must
do so ourselves.

app/utils.h

@@ -8,6 +8,7 @@
 namespace WMUtils {
     bool isRunningX11();
     bool isRunningNvidiaProprietaryDriverX11();
+    bool supportsDesktopGLWithEGL();
     bool isRunningWayland();
     bool isRunningWindowManager();
     bool isRunningDesktopEnvironment();