rpc: add rpc v2 chainSpec to polkadot (#2859)

The [chainSpec RPC API from the v2
spec](https://paritytech.github.io/json-rpc-interface-spec/api/chainSpec.html)
was only added to substrate-node and should be added to polkadot as well

/cc @lexnv

polkadot/node/core/candidate-validation/src/lib.rs

@@ -773,21 +773,21 @@ trait ValidationBackend {
 					if num_death_retries_left > 0 {
 						num_death_retries_left -= 1;
 					} else {
-						break;
+						break
 					},
 
 				Err(ValidationError::PossiblyInvalid(PossiblyInvalidError::JobError(_))) =>
 					if num_job_error_retries_left > 0 {
 						num_job_error_retries_left -= 1;
 					} else {
-						break;
+						break
 					},
 
 				Err(ValidationError::Internal(_)) =>
 					if num_internal_retries_left > 0 {
 						num_internal_retries_left -= 1;
 					} else {
-						break;
+						break
 					},
 
 				Ok(_) | Err(ValidationError::Invalid(_) | ValidationError::Preparation(_)) => break,

polkadot/node/core/candidate-validation/src/tests.rs

@@ -726,7 +726,7 @@ fn candidate_validation_retry_on_error_helper(
 		ExecutorParams::default(),
 		exec_kind,
 		&Default::default(),
-	));
+	))
 }
 
 #[test]