cranelift: Port most of simple_preopt.rs over to the peepmatic DSL

This ports all of the identity, no-op, simplification, and canonicalization
related optimizations over from being hand-coded to the `peepmatic` DSL. This
does not handle the branch-to-branch optimizations or most of the
divide-by-constant optimizations.

cranelift/filetests/src/test_simple_preopt.rs

@@ -38,6 +38,7 @@ impl SubTest for TestSimplePreopt {
             .preopt(isa)
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
         let text = &comp_ctx.func.display(isa).to_string();
+        log::debug!("After simple_preopt:\n{}", text);
         run_filecheck(&text, context)
     }
 }