Introduce new Runtime API endpoint for fetching the validation data (#3728)

* Introduce new Runtime API endpoint

`persisted_validation_data_with_code_hash` that will be used
by the candidate validation subsystem in order to decrease amount
of runtime API requests.

* Node-side part of new runtime API request

* Define code hash getter via macro

* Rename new endpoint to `assumed_validation_data`

* Docs for runtime API impl of new endpoint

* AssumedValidationData specialized request function

* fmt

polkadot/runtime/kusama/src/lib.rs

@@ -1636,6 +1636,16 @@ sp_api::impl_runtime_apis! {
 			parachains_runtime_api_impl::persisted_validation_data::<Runtime>(para_id, assumption)
 		}
 
+		fn assumed_validation_data(
+			para_id: ParaId,
+			expected_persisted_validation_data_hash: Hash,
+		) -> Option<(PersistedValidationData<Hash, BlockNumber>, ValidationCodeHash)> {
+			parachains_runtime_api_impl::assumed_validation_data::<Runtime>(
+				para_id,
+				expected_persisted_validation_data_hash,
+			)
+		}
+
 		fn check_validation_outputs(
 			para_id: ParaId,
 			outputs: primitives::v1::CandidateCommitments,