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/primitives/src/v1/mod.rs

@@ -997,6 +997,14 @@ sp_api::decl_runtime_apis! {
 		fn persisted_validation_data(para_id: Id, assumption: OccupiedCoreAssumption)
 			-> Option<PersistedValidationData<H, N>>;
 
+		/// Returns the persisted validation data for the given `ParaId` along with the corresponding
+		/// validation code hash. Instead of accepting assumption about the para, matches the validation
+		/// data hash against an expected one and yields `None` if they're not equal.
+		fn assumed_validation_data(
+			para_id: Id,
+			expected_persisted_validation_data_hash: Hash,
+		) -> Option<(PersistedValidationData<H, N>, ValidationCodeHash)>;
+
 		/// Checks if the given validation outputs pass the acceptance criteria.
 		fn check_validation_outputs(para_id: Id, outputs: CandidateCommitments) -> bool;