Updated frontend-build to v12 (#962)

* feat: rebase previous frontend-build upgrade

* chore: make welcome message to default to empty

src/instructor-toolbar/InstructorToolbar.jsx

@@ -36,7 +36,7 @@ function getStudioUrl(courseId, unitId) {
   return urlFull;
 }
 
-export default function InstructorToolbar(props) {
+const InstructorToolbar = (props) => {
   // This didMount logic became necessary once we had a page that does a redirect on a quick exit.
   // As a result, it unmounts the InstructorToolbar (which will be remounted by the new component),
   // but the InstructorToolbar's MasqueradeWidget has an outgoing request. Since it is unmounted
@@ -45,6 +45,7 @@ export default function InstructorToolbar(props) {
   // NOTE: This was originally added because of the CourseExit page redirect. Once that page stops
   //   doing a redirect because a CourseExit experience exists for all learners, this could be removed
   const [didMount, setDidMount] = useState(false);
+  // eslint-disable-next-line react-hooks/exhaustive-deps
   useEffect(() => {
     setDidMount(true);
     // Returning this function here will run setDidMount(false) when this component is unmounted
@@ -108,7 +109,7 @@ export default function InstructorToolbar(props) {
       />
     </div>
   ));
-}
+};
 
 InstructorToolbar.propTypes = {
   courseId: PropTypes.string,
@@ -121,3 +122,5 @@ InstructorToolbar.defaultProps = {
   unitId: undefined,
   tab: '',
 };
+
+export default InstructorToolbar;