runtime-api: add validation_code_hash API (#4629)

This is the first step to close
https://github.com/paritytech/polkadot/issues/4524

polkadot/runtime/parachains/src/runtime_api_impl/v1.rs

@@ -389,3 +389,16 @@ pub fn submit_pvf_check_statement<T: paras::Config>(
 pub fn pvfs_require_precheck<T: paras::Config>() -> Vec<ValidationCodeHash> {
 	<paras::Pallet<T>>::pvfs_require_precheck()
 }
+
+/// Returns the validation code hash for the given parachain making the given `OccupiedCoreAssumption`.
+pub fn validation_code_hash<T>(
+	para_id: ParaId,
+	assumption: OccupiedCoreAssumption,
+) -> Option<ValidationCodeHash>
+where
+	T: inclusion::Config,
+{
+	with_assumption::<T, _, _>(para_id, assumption, || {
+		<paras::Pallet<T>>::current_code_hash(&para_id)
+	})
+}