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/node/subsystem-types/src/messages.rs

@@ -611,6 +611,13 @@ pub enum RuntimeApiRequest {
 		OccupiedCoreAssumption,
 		RuntimeApiSender<Option<PersistedValidationData>>,
 	),
+	/// Get the persisted validation data for a particular para along with the current validation code
+	/// hash, matching the data hash against an expected one.
+	AssumedValidationData(
+		ParaId,
+		Hash,
+		RuntimeApiSender<Option<(PersistedValidationData, ValidationCodeHash)>>,
+	),
 	/// Sends back `true` if the validation outputs pass all acceptance criteria checks.
 	CheckValidationOutputs(
 		ParaId,