Introduced token caching to prevent repetetive tokenizing.

Also removed TokenUnderCursor as it's functionality is in the token cache.

Reviewed-by: ckamm

src/plugins/cppeditor/cpphoverhandler.cpp

@@ -232,7 +232,7 @@ void CppHoverHandler::updateHelpIdAndTooltip(TextEditor::ITextEditor *editor, in
         }
 
         // Fetch the expression's code
-        ExpressionUnderCursor expressionUnderCursor;
+        ExpressionUnderCursor expressionUnderCursor(m_modelManager->tokenCache(editor));
         const QString expression = expressionUnderCursor(tc);
 
         const QList<LookupItem> types = typeOfExpression(expression, scope);