Add input dialog to the mixer channel LCD spin box (#7399)

Co-authored-by: saker <sakertooth@gmail.com>

include/MixerChannelLcdSpinBox.h

@@ -50,6 +50,8 @@ protected:
 	void contextMenuEvent(QContextMenuEvent* event) override;
 
 private:
+	void enterValue();
+
 	TrackView * m_tv;
 };