Transpose midi clips in song editor (#6409)

* Transpose midi clips in song editor

* Fix undo stupidity

* Check boundries when transposing clips

and move transpose function to NoteVector

* Avoid update if nothing has changed

* Make getNoteBounds a separate function

* Rename getNoteBounds to boundsForNotes

* bool operator instead of optional + qobject_cast

* Revert "bool operator instead of optional + qobject_cast"

This reverts commit 98c56a96cf.

* qobject_cast and nullopt

include/MidiClipView.h

@@ -73,6 +73,7 @@ protected slots:
 
 	void resetName();
 	void changeName();
+	void transposeSelection();
 
 
 protected:

include/Note.h

@@ -26,6 +26,7 @@
 #ifndef NOTE_H
 #define NOTE_H
 
+#include <optional>
 #include <QVector>
 
 #include "volume.h"
@@ -252,6 +253,18 @@ private:
 typedef QVector<Note *> NoteVector;
 
 
+struct NoteBounds
+{
+	TimePos start;
+	TimePos end;
+	int lowest;
+	int highest;
+};
+
+
+std::optional<NoteBounds> boundsForNotes(const NoteVector& notes);
+
+
 } // namespace lmms
 
 #endif