Add equivocation detector crate and implement clients (#2348) (#2353)

* Split FinalitySyncPipeline and SourceClient

* Move some logic to finality_base

* Add empty equivocation detection clients

* Add equivocation reporting logic to the source client

* Use convenience trait for SubstrateFinalitySyncPipeline

* Define JustificationVerificationContext for GRANDPA

* Equivocation source client: finality_verification_context()

* Equivocation source client: synced_headers_finality_info()

* reuse HeaderFinalityInfo

* Define EquivocationsFinder

* Fix spellcheck

* Address review comments

* Avoid equivocations lookup errors

bridges/primitives/test-utils/src/keyring.rs

@@ -16,10 +16,11 @@
 
 //! Utilities for working with test accounts.
 
+use bp_header_chain::{justification::JustificationVerificationContext, AuthoritySet};
 use codec::Encode;
 use ed25519_dalek::{Keypair, PublicKey, SecretKey, Signature};
 use finality_grandpa::voter_set::VoterSet;
-use sp_consensus_grandpa::{AuthorityId, AuthorityList, AuthorityWeight};
+use sp_consensus_grandpa::{AuthorityId, AuthorityList, AuthorityWeight, SetId};
 use sp_runtime::RuntimeDebug;
 use sp_std::prelude::*;
 
@@ -78,6 +79,11 @@ pub fn voter_set() -> VoterSet<AuthorityId> {
 	VoterSet::new(authority_list()).unwrap()
 }
 
+/// Get a valid justification verification context for a GRANDPA round.
+pub fn verification_context(set_id: SetId) -> JustificationVerificationContext {
+	AuthoritySet { authorities: authority_list(), set_id }.try_into().unwrap()
+}
+
 /// Convenience function to get a list of Grandpa authorities.
 pub fn authority_list() -> AuthorityList {
 	test_keyring().iter().map(|(id, w)| (AuthorityId::from(*id), *w)).collect()