Export StyleSheetMerger class

Used in assetImporter plugin

Task-number: QDS-7652
Change-Id: I2caff28f6a9effbcb2312f120f2ccdc2d0a82a86
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmldesigner/designercore/include/stylesheetmerger.h

@@ -25,6 +25,8 @@
 #ifndef STYLESHEETMERGER_H
 #define STYLESHEETMERGER_H
 
+#include "qmldesignercorelib_global.h"
+
 #include <QString>
 #include <QHash>
 #include <modelnode.h>
@@ -41,8 +43,8 @@ struct ReparentInfo {
     bool alreadyReparented;
 };
 
-
-class StylesheetMerger {
+class QMLDESIGNERCORE_EXPORT StylesheetMerger
+{
 public:
     StylesheetMerger(AbstractView*, AbstractView*);
     void merge();