Fix WASM executor without instance reuse; cleanups and refactoring (#10313)

* Fix WASM executor without instance reuse; cleanups and refactoring

* Align to review comments

* Move the functions for reading/writing memory to `util.rs`

* Only `#[ignore]` the test in debug builds

* More review comments and minor extra comments

substrate/client/executor/wasmtime/build.rs

@@ -0,0 +1,25 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2021 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+use std::env;
+
+fn main() {
+	if let Ok(profile) = env::var("PROFILE") {
+		println!("cargo:rustc-cfg=build_type=\"{}\"", profile);
+	}
+}