Utils: Make Layouting a top level namespace

The whole machinery is now almost only layoutbuilder.{h,cpp},
mostly independent of the rest of Utils. Idea is to finish the
separation to make it stand-alone usable also outside creator.

Change-Id: I958aa667d17ae26b21209f22412309c5307a579c
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/cppeditor/cppcodestylesettingspage.cpp

@@ -175,7 +175,7 @@ public:
         QObject::connect(m_tabSettingsWidget, &TabSettingsWidget::settingsChanged,
                          q, &CppCodeStylePreferencesWidget::slotTabSettingsChanged);
 
-        using namespace Utils::Layouting;
+        using namespace Layouting;
 
         const Group contentGroup {
             title(Tr::tr("Indent")),