Runtime API for checking validation outputs (#1842)

* annoying whitespaces

* update guide

Add `CheckValidationOutputs` runtime api and also change the
candidate-validation stuff

* promote ValidationOutputs to global primitives

i.e. move it from node specific primitives to global v1 primitives. This
will be needed when we share it later in the runtime inclusion module

* refactor acceptance checks in the inclusion module

factor out the common code to share it during the block inclusion and
for the forthcoming CheckValidationOutputs runtime api.

Also note that the acceptance criteria was updated to incorporate checks
that exist now in candidate-validation

* plumb the runtime api outside

* extract validation_data from ValidationOutputs

* use runtime-api to check validation outputs

apart from that refactor, update docs and tidy a bit

* Update the maxium code size

This is to fix a test that performs an upgrade.

polkadot/primitives/src/v1.rs

@@ -303,6 +303,20 @@ pub struct TransientValidationData<N = BlockNumber> {
 	pub code_upgrade_allowed: Option<N>,
 }
 
+/// Outputs of validating a candidate.
+#[derive(Encode, Decode)]
+#[cfg_attr(feature = "std", derive(Clone, Debug, Default))]
+pub struct ValidationOutputs {
+	/// The head-data produced by validation.
+	pub head_data: HeadData,
+	/// Upward messages to the relay chain.
+	pub upward_messages: Vec<UpwardMessage>,
+	/// Fees paid to the validators of the relay-chain.
+	pub fees: Balance,
+	/// The new validation code submitted by the execution, if any.
+	pub new_validation_code: Option<ValidationCode>,
+}
+
 /// Commitments made in a `CandidateReceipt`. Many of these are outputs of validation.
 #[derive(PartialEq, Eq, Clone, Encode, Decode)]
 #[cfg_attr(feature = "std", derive(Debug, Default, Hash))]
@@ -666,6 +680,10 @@ sp_api::decl_runtime_apis! {
 		fn persisted_validation_data(para_id: Id, assumption: OccupiedCoreAssumption)
 			-> Option<PersistedValidationData<N>>;
 
+		// TODO: Adding a Runtime API should be backwards compatible... right?
+		/// Checks if the given validation outputs pass the acceptance criteria.
+		fn check_validation_outputs(para_id: Id, outputs: ValidationOutputs) -> bool;
+
 		/// Returns the session index expected at a child of the block.
 		///
 		/// This can be used to instantiate a `SigningContext`.
@@ -689,7 +707,7 @@ sp_api::decl_runtime_apis! {
 		fn candidate_events() -> Vec<CandidateEvent<H>>;
 
 		/// Get the `AuthorityDiscoveryId`s corresponding to the given `ValidatorId`s.
-		/// Currently this request is limited to validators in the current session. 
+		/// Currently this request is limited to validators in the current session.
 		///
 		/// We assume that every validator runs authority discovery,
 		/// which would allow us to establish point-to-point connection to given validators.