Respect build options in export dialogs (#3714)

* Respect build options in ExportProjectDialog

* Use QItem user data instead of hard ordering to identify export format in ExportProjectDialog

* For compatibility with QVariant, ExportFileFormats is now explicitly an int.

* Don't break out of format identifier loop prematurely in Song export.

include/ProjectRenderer.h

@@ -35,7 +35,7 @@ class ProjectRenderer : public QThread
 {
 	Q_OBJECT
 public:
-	enum ExportFileFormats
+	enum ExportFileFormats: int
 	{
 		WaveFile,
 		OggFile,