Represents this player's personal completion status for the Activity under a
Milestone, if the activity has trackable completion and progress information. (
most activities won't, or the concept won't apply. For instance, it makes sense
to talk about a tier of a raid as being Completed or having progress, but it
doesn't make sense to talk about a Crucible Playlist in those terms.
If the Activity has discrete "phases" that we can track, that info will be here.
Otherwise, this value will be NULL. Note that this is a list and not a
dictionary: the order implies the ascending order of phases or progression in
this activity.
Represents this player's personal completion status for the Activity under a Milestone, if the activity has trackable completion and progress information. ( most activities won't, or the concept won't apply. For instance, it makes sense to talk about a tier of a raid as being Completed or having progress, but it doesn't make sense to talk about a Crucible Playlist in those terms.