Clang: Move unexported classes to Internal

Change-Id: I3ea197b734f146d4b11431aaf927aed9be7d8756
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/clangcodemodel/clangtextmark.cpp

@@ -51,6 +51,7 @@
 using namespace Utils;
 
 namespace ClangCodeModel {
+namespace Internal {
 
 namespace {
 
@@ -228,8 +229,6 @@ void ClangTextMark::updateIcon(bool valid)
 
 bool ClangTextMark::addToolTipContent(QLayout *target) const
 {
-    using Internal::ClangDiagnosticWidget;
-
     QWidget *widget = ClangDiagnosticWidget::createWidget({m_diagnostic},
                                                           ClangDiagnosticWidget::ToolTip);
     target->addWidget(widget);
@@ -243,5 +242,6 @@ void ClangTextMark::removedFromEditor()
     m_removedFromEditorHandler(this);
 }
 
+} // namespace Internal
 } // namespace ClangCodeModel