Separate wasmi and wasmer sandbox implementations into their own modules (#10563)

* Moves wasmi specific `ImportResolver` and `MemoryTransfer` impls to submodule

* Splits context store environmental, moves impl `Externals` to wasmi backend

* Adds wasmer sandbox backend stub module

* Move sandbox impl code to backend specific modules

* Moves wasmi stuff

* Fixes value conversion

* Makes it all compile

* Remove `with_context_store`

* Moves `WasmerBackend` to the impl

* Reformat the source

* Moves wasmer MemoryWrapper

* Reformats the source

* Fixes mutability

* Moves backend impls to a submodule

* Fix visibility

* Reformat the source

* Feature gate wasmer backend module

* Moves wasmi memory allocation to backend module

* Rename WasmerBackend to Backend

* Refactor dispatch result decoding, get rid of Wasmi types in common sandbox code

* Reformat the source

* Remove redundant prefixes in backend functions

* Remove wasmer-sandbox from default features

* Post-review changes

* Add conversion soundness proof

* Remove redundant prefix

* Removes now redundant clone_inner

* Add `Error::SandboxBackend`, refactor invoke result

* Fix comments

* Rename `Error::SandboxBackend` to `Sandbox`

* Simplifies logic in `wasmer_backend::invoke`

* Fixes memory management

substrate/client/executor/wasmtime/src/host.rs

@@ -221,7 +221,6 @@ impl<'a> Sandbox for HostContext<'a> {
 		let args = Vec::<sp_wasm_interface::Value>::decode(&mut args)
 			.map_err(|_| "Can't decode serialized arguments for the invocation")?
 			.into_iter()
-			.map(Into::into)
 			.collect::<Vec<_>>();
 
 		let instance = self.sandbox_store().instance(instance_id).map_err(|e| e.to_string())?;