Candidate Validation Subsystem (#1432)

* skeleton for candidate-validation

* add to workspace

* implement candidate validation logic

* guide: note occupied-core assumption for candidate validation

* adjust message doc

* wire together `run` asynchronously

* add a Subsystem implementation

* clean up a couple warnings

* fix compilation errors due to merge

* improve candidate-validation.md

* remove old reference to subsystem-test helpers crate

* update Cargo.lock

* add a couple new Runtime API methods

* add a candidate validation message

* fetch validation data from the chain state

* some tests for assumption checking

* make spawn_validate_exhaustive mockable

* more tests on the error handling side

* fix all other grumbles except for wasm validation API change

* wrap a SpawnNamed in candidate-validation

* warn

* amend guide

* squanch warning

* remove duplicate after merge

polkadot/Cargo.lock

@@ -4635,6 +4635,24 @@ dependencies = [
  "wasm-timer",
 ]
 
+[[package]]
+name = "polkadot-node-core-candidate-validation"
+version = "0.1.0"
+dependencies = [
+ "assert_matches",
+ "derive_more 0.99.9",
+ "futures 0.3.5",
+ "log 0.4.8",
+ "parity-scale-codec",
+ "polkadot-node-primitives",
+ "polkadot-node-subsystem",
+ "polkadot-parachain",
+ "polkadot-primitives",
+ "sp-blockchain",
+ "sp-core",
+ "sp-keyring",
+]
+
 [[package]]
 name = "polkadot-node-core-proposer"
 version = "0.1.0"