This commit introduces the changes needed for XBlocks in Blockstore to save
their user state into CSM. Before this commit, all student state for Blockstore
blocks was ephemeral (in-process dict store).
Notes:
* The main risk factor of this PR is that it adds non-course keys to the
course_id field in CSM. If any code (like analytics?) reads course keys
directly out of CSM and doesn't have graceful handling for key types it
doesn't recognize, it could cause an issue. With the included changes to
opaque-keys, calling CourseKey.from_string(...) on these values will raise
InvalidKeyError since they're not CourseKeys. (But calling
LearningContextKey.from_string(...) will work for both course and library
keys.)
* This commit introduces a slight regression for the Studio view of XBlocks in
Blockstore content libraries: their state is now lost from request to request.
I have a follow up PR to give them a proper studio-appropriate state store,
but I want to review it separately so it doesn't hold up this PR and we can
test this PR on its own.
1382bf8720