Lv2Proc: Sort scale point maps (#6859)

lilv can return the scale points in randomized order, and so the linked
models (of stereo effects wit 2 `Lv2Proc`) may have different scale
points. This would mean that the same combo enumeration value would have
different float values in linked models. This problem is fixed by
sorting the scale values.

Also, it is more natural for users if scale points are enumerated in a
numerical order.

include/Lv2Basics.h

@@ -47,8 +47,14 @@ struct LilvNodesDeleter
 	void operator()(LilvNodes* n) { lilv_nodes_free(n); }
 };
 
+struct LilvScalePointsDeleter
+{
+	void operator()(LilvScalePoints* s) { lilv_scale_points_free(s); }
+};
+
 using AutoLilvNode = std::unique_ptr<LilvNode, LilvNodeDeleter>;
 using AutoLilvNodes = std::unique_ptr<LilvNodes, LilvNodesDeleter>;
+using AutoLilvScalePoints = std::unique_ptr<LilvScalePoints, LilvScalePointsDeleter>;
 
 /**
 	Return QString from a plugin's node, everything will be freed automatically