Currently, mod_lti does not support FEATURE_GROUPINGS. This means that if we use the options to send group information to the other tool, there may be problems.

1. The whole point of Moodle's Groupings features is that you can have lots of different sets of groups set up, and then for each activity, you can indicate which groups should be used within that activity. This standard features makes sense in relation to LTI activities too, and we can support it, so we should.
2. Also there might be privacy concerns with some of the groups. For example you might have a grouping with groups used to allow certain students additional time in the course quizzes using Group overrides. Which students are in those groups is sensitive information which should not be sent to a third-party tool. Supporting this Moodle setting solves that too.

I think that to implement this, we just need to:

1. return true for FEATURE_GROUPINGS in lti_supports.
2. Check all the places in mod_lti that use the Groups API, to make sure they are using it correctly for an activity in the normal way, including passing $cm->grouping.