Clang: Clean up diagnostic widget

* Use a single QLabel - No need for all the QLabels we used. Also, a
  single QLabel enables selecting and copying all the diagnostics, which
  is handy when displayed in the info bar.
* Avoid call to Utils::ToolTip::hideImmediately() if the location is
  clicked from the info bar.
* Simplify code and API

Change-Id: Ib991364e4d6f40ef02dada8ebbb90fe6ff8ae1a1
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangdiagnostictooltipwidget.h

@@ -34,15 +34,13 @@ QT_END_NAMESPACE
 namespace ClangCodeModel {
 namespace Internal {
 
-struct DisplayHints {
-    bool showMainDiagnosticHeader = true;
-    bool showFileNameInMainDiagnostic = false;
-    bool enableClickableFixits = true;
-};
+class ClangDiagnosticWidget {
+public:
+    enum Destination { ToolTip, InfoBar };
 
-void addToolTipToLayout(const ClangBackEnd::DiagnosticContainer &diagnostic,
-                        QLayout *target,
-                        const DisplayHints &displayHints = DisplayHints());
+    static QWidget *create(const QVector<ClangBackEnd::DiagnosticContainer> &diagnostics,
+                           const Destination &destination);
+};
 
 } // namespace Internal
 } // namespace ClangCodeModel