QmlJsEditor/QmlJsTools: Use override consistently

clang-tidy fixes from modernize-use-override check.

Change-Id: I29716dcf73946b5762568d349a3f5a3da4f656e6
Reviewed-by: Marco Benelli <marco.benelli@qt.io>

src/plugins/qmljseditor/qmljsquickfix.h

@@ -57,7 +57,7 @@ public:
      */
     explicit QmlJSQuickFixOperation(const QmlJSQuickFixInterface &interface, int priority = -1);
 
-    virtual void perform();
+    void perform() override;
 
 protected:
     typedef Utils::ChangeSet::Range Range;