Bridge: slash destination may be an explicit account (#4106)

Extracted to a separate PR as requested here:
https://github.com/paritytech/parity-bridges-common/pull/2873#discussion_r1562459573

bridges/primitives/relayers/src/lib.rs

@@ -19,7 +19,7 @@
 #![warn(missing_docs)]
 #![cfg_attr(not(feature = "std"), no_std)]
 
-pub use registration::{Registration, StakeAndSlash};
+pub use registration::{ExplicitOrAccountParams, Registration, StakeAndSlash};
 
 use bp_messages::LaneId;
 use bp_runtime::{ChainId, StorageDoubleMapKeyProvider};