Add candidate info to OccupiedCore (#2134)

* guide: add candidate information to OccupiedCore

* add descriptor and hash to occupied core type

* guide: add candidate hash to inclusion

* runtime: return candidate info in core state

* bitfield signing: stop querying runtime as much

* minimize going to runtime in availability distribution

* fix availability distribution tests

* guide: remove para ID from Occupied core

* get all crates compiling

polkadot/roadmap/implementers-guide/src/runtime-api/availability-cores.md

@@ -12,8 +12,7 @@ This is all the information that a validator needs about scheduling for the curr
 
 ```rust
 struct OccupiedCore {
-    /// The ID of the para occupying the core.
-    para_id: ParaId,
+    // NOTE: this has no ParaId as it can be deduced from the candidate descriptor.
     /// If this core is freed by availability, this is the assignment that is next up on this
     /// core, if any. None if there is nothing queued for this core.
     next_up_on_available: Option<ScheduledCore>,
@@ -31,6 +30,10 @@ struct OccupiedCore {
     availability: Bitfield,
     /// The group assigned to distribute availability pieces of this candidate.
     group_responsible: GroupIndex,
+    /// The hash of the candidate occupying the core.
+    candidate_hash: CandidateHash,
+    /// The descriptor of the candidate occupying the core.
+    candidate_descriptor: CandidateDescriptor,
 }
 
 struct ScheduledCore {