* fix: main page course listing
The course is visible on the main page right after creation when the feature toggle `CREATE_COURSE_WITH_DEFAULT_ENROLLMENT_START_DATE` is on.
So anonymous users can see them and access the course about page
for the courses without valid data (e.g. they will see the default
course overview)
When courses list filtering is processed it checks the `see_exists`
permission for the anonymous user.
Actually, `see_exists` means `can_load` OR `can_enroll`.
`can_load` is False in our case because the course start in the future.
But `can_enroll` returns True because the course's enrollment_start
and enrollment_end dates are blank:
```
enrollment_start = courselike.enrollment_start or datetime.min.replace(tzinfo=UTC)
enrollment_end = courselike.enrollment_end or datetime.max.replace(tzinfo=UTC)
if enrollment_start < now < enrollment_end:
debug("Allow: in enrollment period")
return ACCESS_GRANTED
```
Set the enrollment_start the same as a course start by default
This commit replaces the learning_assistant_launch_url field of the CoursewareInformation view of the courseware API with a learning_assistant_enabled field. learning_assistant_enabled is a boolean that represents whether the Xpert Learning Assistant is enabled for the requesting user, based on the associated CourseWaffleFlag. This change is necessary because we are no longer leveraging the Learning Assistant LTI tool.
* feat: tests for copying units in content_staging app
* chore: convert old tests to pytest style
* feat: make pasting units work (in Studio backend API)
* refactor: make XmlMixin.parse_xml more like standard XBlock behavior
* chore: typing + fixes for content_staging
* chore: typing + fixes for learning_sequences
* chore: typing + fixes for content_libraries
* chore: typing + fixes for new XBlock runtime
* feat: type hinting more code with mypy
This re-applies commit 36cc415 with handling an invalid context_key in the
`PartitionService`. It can happen when rendering a `LibraryContentBlock` in
Studio because this service is initialized by the modulestore when validating
an XBlock to gather its error messages in the `studio_xblock_wrapper`.
