mandclu: Dynamic Entity Query Based on Moderation State

As part of my ongoing work on the Event Platform modules for organizing DrupalCamps and similar events, I wanted to add to the recently introduced Scheduler interface, by allowing a site builder to specify a list of workflow (content moderation) states that would be used to restrict which sessions (or other content types) to list. After, it wouldn’t make sense to ask an editor to have to pick through the rejected sessions as part of the scheduling interface.