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/runtime/src/unquote.rs

@@ -0,0 +1,44 @@
+//! Unquote operator definition.
+
+peepmatic_traits::define_operator! {
+    /// Compile-time unquote operators.
+    ///
+    /// These are used in the right-hand side to perform compile-time evaluation of
+    /// constants matched on the left-hand side.
+    #[allow(missing_docs)]
+    UnquoteOperator {
+        band => Band {
+            parameters(iNN, iNN);
+            result(iNN);
+        }
+        bor => Bor {
+            parameters(iNN, iNN);
+            result(iNN);
+        }
+        bxor => Bxor {
+            parameters(iNN, iNN);
+            result(iNN);
+        }
+        iadd => Iadd {
+            parameters(iNN, iNN);
+            result(iNN);
+        }
+        imul => Imul {
+            parameters(iNN, iNN);
+            result(iNN);
+        }
+        isub => Isub {
+            parameters(iNN, iNN);
+            result(iNN);
+        }
+        log2 => Log2 {
+            parameters(iNN);
+            result(iNN);
+        }
+        neg => Neg {
+            parameters(iNN);
+            result(iNN);
+        }
+    }
+    parse_cfg(feature = "construct");
+}