Refactor NativeExecutor to support multiple Wasm execution methods (#3677)

* executor: Move definitions of externals out of wasm_executor module.

* executor: Create WasmRuntime trait.

This will be used to decouple the runtime cache from wasmi execution.

* executor: Remove WasmExecutor and move methods to wasmi_execution.

These will now be crate-internal functions and there is no need
for the struct.

* executor: Set default default_heap_pages in NativeExecutor.

* cli: CLI configuration for Wasm execution method.

* executor: Remove wasmi-specific code from wasm_runtime.

* Respond to review comments.

substrate/core/service/src/builder.rs

@@ -167,7 +167,10 @@ where TGen: RuntimeGenesis, TCSExt: Extension {
 			pruning: config.pruning.clone(),
 		};
 
-		let executor = NativeExecutor::<TExecDisp>::new(config.default_heap_pages);
+		let executor = NativeExecutor::<TExecDisp>::new(
+			config.wasm_method,
+			config.default_heap_pages,
+		);
 
 		let fork_blocks = config.chain_spec
 			.extensions()
@@ -239,7 +242,10 @@ where TGen: RuntimeGenesis, TCSExt: Extension {
 			pruning: config.pruning.clone(),
 		};
 
-		let executor = NativeExecutor::<TExecDisp>::new(config.default_heap_pages);
+		let executor = NativeExecutor::<TExecDisp>::new(
+			config.wasm_method,
+			config.default_heap_pages,
+		);
 
 		let db_storage = client_db::light::LightStorage::new(db_settings)?;
 		let light_blockchain = client::light::new_light_blockchain(db_storage);

substrate/core/service/src/config.rs

@@ -19,6 +19,7 @@
 pub use client::ExecutionStrategies;
 pub use client_db::PruningMode;
 pub use network::config::{ExtTransport, NetworkConfiguration, Roles};
+pub use substrate_executor::WasmExecutionMethod;
 
 use std::{path::PathBuf, net::SocketAddr};
 use transaction_pool;
@@ -60,6 +61,8 @@ pub struct Configuration<C, G, E = NoExtension> {
 	pub custom: C,
 	/// Node name.
 	pub name: String,
+	/// Wasm execution method.
+	pub wasm_method: WasmExecutionMethod,
 	/// Execution strategies.
 	pub execution_strategies: ExecutionStrategies,
 	/// RPC over HTTP binding address. `None` if disabled.
@@ -116,6 +119,7 @@ impl<C, G, E> Configuration<C, G, E> where
 			state_cache_child_ratio: Default::default(),
 			custom: Default::default(),
 			pruning: PruningMode::default(),
+			wasm_method: WasmExecutionMethod::Interpreted,
 			execution_strategies: Default::default(),
 			rpc_http: None,
 			rpc_ws: None,