fix: hide sequences & sections when access is restricted in units through cohorts (#33191)

This does two major things:

* Removes subsections from a student's course outline if the
  subsection's units are all restricted to a cohort that the student
  is not a part of (see CohortPartitionGroupsOutlineProcessor).
* Removes sections from the course outline if the user is not allowed
  to see any of its child subsections.

lms/djangoapps/course_home_api/outline/views.py

@@ -303,9 +303,20 @@ class OutlineTabView(RetrieveAPIView):
             )
             available_seq_ids = {str(usage_key) for usage_key in user_course_outline.sequences}
 
+            available_section_ids = {str(section.usage_key) for section in user_course_outline.sections}
+
+            # course_blocks is a reference to the root of the course,
+            # so we go through the chapters (sections) and keep only those
+            # which are part of the outline.
+            course_blocks['children'] = [
+                chapter_data
+                for chapter_data in course_blocks.get('children', [])
+                if chapter_data['id'] in available_section_ids
+            ]
+
             # course_blocks is a reference to the root of the course, so we go
             # through the chapters (sections) to look for sequences to remove.
-            for chapter_data in course_blocks.get('children', []):
+            for chapter_data in course_blocks['children']:
                 chapter_data['children'] = [
                     seq_data
                     for seq_data in chapter_data['children']