Clang: Use CppHoverHandler for diagnostic tooltips

We used to call QTextCharFormat::setToolTip from the ExtraSelection to
install the diagnostic tooltip. Since this allows to set only text
tooltips and we would like to introduce a custom tooltip widget for
diagnostics, make use of CppHoverHandler, which is more flexible.

Change-Id: Ia1b2c3c50810596ce4a3a025002e6e4efd8789db
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

src/plugins/cpptools/baseeditordocumentprocessor.cpp

@@ -58,6 +58,15 @@ BaseEditorDocumentProcessor::extraRefactoringOperations(const TextEditor::Assist
     return TextEditor::QuickFixOperations();
 }
 
+bool BaseEditorDocumentProcessor::hasDiagnosticsAt(uint, uint) const
+{
+    return false;
+}
+
+void BaseEditorDocumentProcessor::showDiagnosticTooltip(const QPoint &, QWidget *, uint, uint) const
+{
+}
+
 void BaseEditorDocumentProcessor::runParser(QFutureInterface<void> &future,
                                             BaseEditorDocumentParser::Ptr parser,
                                             const WorkingCopy workingCopy)