QmlDesigner: add item library plugins path again

  - This was accidentally removed by the patch which removed
    the old pluginmanager

Change-Id: I990d05555bbfe519c72a1d34cffdfc00360d88c1
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@theqtcompany.com>

src/plugins/qmldesigner/qmldesignerplugin.cpp

@@ -30,6 +30,7 @@
 #include "settingspage.h"
 #include "designmodecontext.h"
 
+#include <metainfo.h>
 #include <connectionview.h>
 #include <sourcetool/sourcetool.h>
 #include <colortool/colortool.h>
@@ -187,6 +188,13 @@ bool QmlDesignerPlugin::initialize(const QStringList & /*arguments*/, QString *e
                 switchTextDesignAction, QmlDesigner::Constants::SWITCH_TEXT_DESIGN, switchContext);
     command->setDefaultKeySequence(QKeySequence(Qt::Key_F4));
 
+    // adding default path to item library plugins
+    const QString pluginPath = Utils::HostOsInfo::isMacHost()
+            ? QString(QCoreApplication::applicationDirPath() + "/../PlugIns/QmlDesigner")
+            : QString(QCoreApplication::applicationDirPath() + "/../"
+                      + QLatin1String(IDE_LIBRARY_BASENAME) + "/qtcreator/plugins/qmldesigner");
+    MetaInfo::setPluginPaths(QStringList(pluginPath));
+
     createDesignModeWidget();
     connect(switchTextDesignAction, &QAction::triggered, this, &switchTextDesign);