GtkWidget for the priority of extension under Extension Tab.

The new structure :
 PriorityMergedHBox
  --OptionalBox
    --ToolBoxExtension
      --Extension1
  --OptionalBox
.....

Change-Id: I72760e4f0d60eb6f1f82c1e928601d41a2e4b6ce
Reviewed-on: https://gerrit.libreoffice.org/76987
Tested-by: Jenkins
Reviewed-by: Szymon Kłos <szymon.klos@collabora.com>
diff --git a/vcl/source/window/builder.cxx b/vcl/source/window/builder.cxx
index 3b7db3e..b4678d2 100644
--- a/vcl/source/window/builder.cxx
+++ b/vcl/source/window/builder.cxx
@@ -2187,7 +2187,10 @@
    }
    else if (name == "NotebookBarAddonsToolMergePoint")
    {
        NotebookBarAddonsMerger::MergeNotebookBarAddons(pParent, m_xFrame, m_pNotebookBarAddonsItem);
        customMakeWidget pFunction = nullptr;
        ModuleMap::iterator aI = g_aModuleMap.find("libsfxlo.so");
        pFunction = reinterpret_cast<customMakeWidget>(aI->second->getFunctionSymbol("makeNotebookbarToolBox"));
        NotebookBarAddonsMerger::MergeNotebookBarAddons( pParent, pFunction, m_xFrame, m_pNotebookBarAddonsItem, rMap );
        return nullptr;
    }
    else if (name == "GtkToolButton" || name == "GtkMenuToolButton" ||