signed wrapper (#1283)

* add signed wrapper, typedef SignedStatement

* typedef SignedAvailabilityBitfield

* implement Signed wrapper

This is strictly an addition as of this commit; nothing is yet
changed in existing behavior.

* inline getters, remove review comment

* move EncodeAs, Signed from node::primitives to primitives::parachain

* Refactor SignedAvailabilityBitfield to use Signed

* don't double-encode real payload

This isn't an ideal solution, because it depends on the
implementation details of how SCALE encodes tuples, but OTOH
that behavior seems unlikely to change anytime soon.

* fix build errors

* cause the runtime to build properly with the new changes

Not sure why cargo check didn't catch this earlier; oh well.

* fix runtime tests and separate SignedStatement from SignedFullStatement

* better explain why CompactStatement exists

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

polkadot/runtime/common/src/parachains.rs

@@ -41,7 +41,7 @@ use primitives::{
 	Balance,
 	BlockNumber,
 	parachain::{
-		Id as ParaId, Chain, DutyRoster, AttestedCandidate, Statement, ParachainDispatchOrigin,
+		Id as ParaId, Chain, DutyRoster, AttestedCandidate, CompactStatement as Statement, ParachainDispatchOrigin,
 		UpwardMessage, ValidatorId, ActiveParas, CollatorId, Retriable, OmittedValidationData,
 		CandidateReceipt, GlobalValidationSchedule, AbridgedCandidateReceipt,
 		LocalValidationData, Scheduling, ValidityAttestation, NEW_HEADS_IDENTIFIER, PARACHAIN_KEY_TYPE_ID,

polkadot/runtime/common/src/registrar.rs

@@ -673,7 +673,7 @@ mod tests {
 	use primitives::{
 		parachain::{
 			ValidatorId, Info as ParaInfo, Scheduling, LOWEST_USER_ID, AttestedCandidate,
-			CandidateReceipt, HeadData, ValidityAttestation, Statement, Chain,
+			CandidateReceipt, HeadData, ValidityAttestation, CompactStatement as Statement, Chain,
 			CollatorPair, CandidateCommitments,
 		},
 		Balance, BlockNumber, Header, Signature,