WasmExecutor takes a cache directory (#8057)

That is useful for executors like wasmtime which produces compiled code
and can actually benefit from caching under some circumstances

substrate/client/executor/src/lib.rs

@@ -80,6 +80,7 @@ mod tests {
 			Some(8),
 			sp_io::SubstrateHostFunctions::host_functions(),
 			8,
+			None,
 		);
 		let res = executor.call_in_wasm(
 			&wasm_binary_unwrap()[..],