Refactor sp-sandbox; make sure both sandbox executors are always tested (#10173)

* sp-sandbox: convert executors into normal `mod`s instead of using `include!`

* sp-sandbox: run `cargo fmt` on `host_executor.rs`

* sp-sandbox: abstract away the executors behind traits

* sp_sandbox: always compile both executors when possible

* sc-executor: make sure all sandbox tests run on both sandbox executors

* sc-executor: fix brainfart: actually call into the sandbox through the trait

* sc-runtime-test: fix cargo fmt

* sc-runtime-test: deduplicate executor-specific sandbox test entrypoints

* sc-executor: test each sandbox executor in a separate test

* cargo fmt (Github's conflict resolving thingy broke indentation)

substrate/frame/contracts/src/benchmarking/sandbox.rs

@@ -20,7 +20,10 @@
 /// ! environment that provides the seal interface as imported functions.
 use super::{code::WasmModule, Config};
 use sp_core::crypto::UncheckedFrom;
-use sp_sandbox::{EnvironmentDefinitionBuilder, Instance, Memory};
+use sp_sandbox::{
+	default_executor::{EnvironmentDefinitionBuilder, Instance, Memory},
+	SandboxEnvironmentBuilder, SandboxInstance,
+};
 
 /// Minimal execution environment without any exported functions.
 pub struct Sandbox {