Add relay storage root to persisted validation data (#2161)

* Cont.: Implement the state root obtaining during inclusion

During inclusion now we obtain the storage root by passing it through
the inclusion_inherent.

* Fix tests

* Bump rococo spec version

* Reorder the parent header into the end

of the inclusion inherent.

When the parent header is in the beginning, it shifts the other two
fields, so that a previous version won't be able to decode that. If
we put the parent header in the end, the other two fields will stay
at their positions, thus make it possible to decode with the previous
version.

That allows us to perform upgrade of rococo runtime without needing of
simultanuous upgrade of nodes and runtime, or restart of the network.

* Squash a stray tab

polkadot/roadmap/implementers-guide/src/runtime/inclusion.md

@@ -59,7 +59,7 @@ All failed checks should lead to an unrecoverable error making the block invalid
   1. For each applied bit of each availability-bitfield, set the bit for the validator in the `CandidatePendingAvailability`'s `availability_votes` bitfield. Track all candidates that now have >2/3 of bits set in their `availability_votes`. These candidates are now available and can be enacted.
   1. For all now-available candidates, invoke the `enact_candidate` routine with the candidate and relay-parent number.
   1. Return a list of freed cores consisting of the cores where candidates have become available.
-* `process_candidates(BackedCandidates, scheduled: Vec<CoreAssignment>, group_validators: Fn(GroupIndex) -> Option<Vec<ValidatorIndex>>)`:
+* `process_candidates(parent_storage_root, BackedCandidates, scheduled: Vec<CoreAssignment>, group_validators: Fn(GroupIndex) -> Option<Vec<ValidatorIndex>>)`:
   1. check that each candidate corresponds to a scheduled core and that they are ordered in the same order the cores appear in assignments in `scheduled`.
   1. check that `scheduled` is sorted ascending by `CoreIndex`, without duplicates.
   1. check that there is no candidate pending availability for any scheduled `ParaId`.

polkadot/roadmap/implementers-guide/src/runtime/inclusioninherent.md

@@ -16,11 +16,13 @@ Included: Option<()>,
 
 ## Entry Points
 
-* `inclusion`: This entry-point accepts two parameters: [`Bitfields`](../types/availability.md#signed-availability-bitfield) and [`BackedCandidates`](../types/backing.md#backed-candidate).
+* `inclusion`: This entry-point accepts three parameters: The relay-chain parent block header, [`Bitfields`](../types/availability.md#signed-availability-bitfield) and [`BackedCandidates`](../types/backing.md#backed-candidate).
+    1. Hash the parent header and make sure that it corresponds to the block hash of the parent (tracked by the `frame_system` FRAME module),
     1. The `Bitfields` are first forwarded to the `Inclusion::process_bitfields` routine, returning a set of freed cores. Provide a `Scheduler::core_para` as a core-lookup to the `process_bitfields` routine. Annotate each of these freed cores with `FreedReason::Concluded`.
     1. If `Scheduler::availability_timeout_predicate` is `Some`, invoke `Inclusion::collect_pending` using it, and add timed-out cores to the free cores, annotated with `FreedReason::TimedOut`.
     1. Invoke `Scheduler::schedule(freed)`
-	1. Invoke the `Inclusion::process_candidates` routine with the parameters `(backed_candidates, Scheduler::scheduled(), Scheduler::group_validators)`.
+    1. Extract `parent_storage_root` from the parent header,
+    1. Invoke the `Inclusion::process_candidates` routine with the parameters `(parent_storage_root, backed_candidates, Scheduler::scheduled(), Scheduler::group_validators)`.
     1. Call `Scheduler::occupied` using the return value of the `Inclusion::process_candidates` call above, first sorting the list of assigned core indices.
     1. Call the `Ump::process_pending_upward_messages` routine to execute all messages in upward dispatch queues.
     1. If all of the above succeeds, set `Included` to `Some(())`.