peepmatic: Be generic over the operator type

This lets us avoid the cost of `cranelift_codegen::ir::Opcode` to
`peepmatic_runtime::Operator` conversion overhead, and paves the way for
allowing Peepmatic to support non-clif optimizations (e.g. vcode optimizations).

Rather than defining our own `peepmatic::Operator` type like we used to, now the
whole `peepmatic` crate is effectively generic over a `TOperator` type
parameter. For the Cranelift integration, we use `cranelift_codegen::ir::Opcode`
as the concrete type for our `TOperator` type parameter. For testing, we also
define a `TestOperator` type, so that we can test Peepmatic code without
building all of Cranelift, and we can keep them somewhat isolated from each
other.

The methods that `peepmatic::Operator` had are now translated into trait bounds
on the `TOperator` type. These traits need to be shared between all of
`peepmatic`, `peepmatic-runtime`, and `cranelift-codegen`'s Peepmatic
integration. Therefore, these new traits live in a new crate:
`peepmatic-traits`. This crate acts as a header file of sorts for shared
trait/type/macro definitions.

Additionally, the `peepmatic-runtime` crate no longer depends on the
`peepmatic-macro` procedural macro crate, which should lead to faster build
times for Cranelift when it is using pre-built peephole optimizers.

cranelift/peepmatic/crates/macro/src/into_dyn_ast_ref.rs

@@ -13,7 +13,7 @@ pub fn derive_into_dyn_ast_ref(input: &DeriveInput) -> Result<impl quote::ToToke
     let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
 
     Ok(quote! {
-        impl #impl_generics From<&'a #ty #ty_generics> for DynAstRef<'a> #where_clause {
+        impl #impl_generics From<&'a #ty #ty_generics> for DynAstRef<'a, TOperator> #where_clause {
             #[inline]
             fn from(x: &'a #ty #ty_generics) -> Self {
                 Self::#ty(x)