Prerequisites for validate_block in Cumulus (#1926)

* Adds benchmark for direct/indirect wasm function calls

* Store the benchmark function pointer in a `Cell`

* Add some documentation

* Make function implementations exchangeable

* Add parachain stub

* Add macro for registering the `validate_block` function

* Make all functions replace-able by unimplemented

* Some more refactoring

* Adds tests for executing empty parachain block

* Work on a new test with empty witness data

* Don't exchange `ext_print_*` stuff

* Some cleanup and one more function for `validate_block`

* More tests and more functions

* Fixes after merging master

* Use `parity-codec` `derive` feature

* CHange implementation of `wasm-nice-panic-message`

* Move `parachain` stuff to cumulus

* Updated wasm files

* Integrate feedback

* Switch to `ExchangeableFunction` struct

* More fixes

* Switch to Cell and panic on multiple replaces

* Increase `impl_version`

* Fix shifting

* Make the API more verbose of `ExchangeableFunction`

* Increase `impl_version`

substrate/core/test-runtime/Cargo.toml

@@ -20,6 +20,7 @@ runtime_io = { package = "sr-io", path = "../sr-io", default-features = false }
 runtime_primitives = { package = "sr-primitives", path = "../sr-primitives", default-features = false }
 runtime_version = { package = "sr-version", path = "../sr-version", default-features = false }
 runtime_support = { package = "srml-support", path = "../../srml/support", default-features = false }
+executive = { package = "srml-executive", path = "../../srml/executive", default-features = false }
 cfg-if = "0.1.6"
 
 [dev-dependencies]
@@ -44,4 +45,5 @@ std = [
 	"runtime_primitives/std",
 	"runtime_version/std",
 	"consensus_aura/std",
+	"executive/std",
 ]