feat: Use legacy_web_url to redirect to legacy courseware (#404)

As part of making the new courseware experience the
default for staff, the LMS /jump_to/ links that are
exposed by the Course Blocks API via the `lms_web_url`
field will soon direct users to whichever experience
is active to them (instead of always directing to
the legacy experience & relying on the learner
redirect).

Because of this, the MFE can no longer rely on
`lms_web_url` to land a staff user to the legacy
experience. However, the aformentioned change
will also introduce a `legacy_web_url` field
to the API, which we *can* use for this purpose.

TNL-7796

src/shared/data/__factories__/block.factory.js

@@ -48,7 +48,7 @@ Factory.define('block')
   )
   .attr(
     'lms_web_url',
-    ['lms_web_url', 'host', 'courseId', 'id'],
+    ['legacy_web_url', 'host', 'courseId', 'id'],
     (url, host, courseId, id) => {
       if (url) {
         return url;
@@ -56,4 +56,15 @@ Factory.define('block')
 
       return `${host}/courses/${courseId}/jump_to/${id}`;
     },
+  )
+  .attr(
+    'legacy_web_url',
+    ['legacy_web_url', 'host', 'courseId', 'id'],
+    (url, host, courseId, id) => {
+      if (url) {
+        return url;
+      }
+
+      return `${host}/courses/${courseId}/jump_to/${id}?experience=legacy`;
+    },
   );