winch: Prepare for an update to the wasm-tools crates (#5238)

This commit prepares the `winch` crate for updating `wasm-tools`,
notably changing a bit about how the visitation of operators works. This
moves the function body and wasm validator out of the `CodeGen`
structure and into parameters threaded into the emission of the actual
function.

Additionally the `VisitOperator` implementation was updated to remove
the explicit calls to the validator, favoring instead a macro-generated
solution to guarantee that all validation happens before any translation
proceeds. This means that the `VisitOperator for CodeGen` impl is now
infallible and the various methods have been inlined into the trait
methods as well as removing the `Result<_>`.

Finally this commit updates translation to call `validator.finish(..)`
which is required to perform the final validation steps of the function
body.

winch/src/main.rs

@@ -63,7 +63,7 @@ fn compile(
     let FunctionBodyData { body, validator } = f.1;
     let validator = validator.into_validator(Default::default());
     let buffer = isa
-        .compile_function(&sig, body, validator)
+        .compile_function(&sig, &body, validator)
         .expect("Couldn't compile function");
     for i in buffer {
         println!("{}", i);