Optimizations to egraph framework (#5391)

* Optimizations to egraph framework:

- Save elaborated results by canonical value, not latest value (union
  value). Previously we were artificially skipping and re-elaborating
  some values we already had because we were not finding them in the
  map.

- Make some changes to handling of icmp results: when icmp became
  I8-typed (when bools went away), many uses became `(uextend $I32 (icmp
  $I8 ...))`, and so patterns in lowering backends were no longer
  matching.

  This PR includes an x64-specific change to match `(brz (uextend (icmp
  ...)))` and similarly for `brnz`, but it also takes advantage of the
  ability to write rules easily in the egraph mid-end to rewrite selects
  with icmp inputs appropriately.

- Extend constprop to understand selects in the egraph mid-end.

With these changes, bz2.wasm sees a ~1% speedup, and spidermonkey.wasm
with a fib.js input sees a 16.8% speedup:

```
$ time taskset 1 target/release/wasmtime run --allow-precompiled --dir=. ./spidermonkey.base.cwasm ./fib.js
1346269
taskset 1 target/release/wasmtime run --allow-precompiled --dir=.  ./fib.js  2.14s user 0.01s system 99% cpu 2.148 total
$ time taskset 1 target/release/wasmtime run --allow-precompiled --dir=. ./spidermonkey.egraphs.cwasm ./fib.js
1346269
taskset 1 target/release/wasmtime run --allow-precompiled --dir=.  ./fib.js  1.78s user 0.01s system 99% cpu 1.788 total
```

* Review feedback.

cranelift/codegen/src/isle_prelude.rs

@@ -586,6 +586,26 @@ macro_rules! isle_common_prelude_methods {
             }
         }
 
+        #[inline]
+        fn intcc_reverse(&mut self, cc: &IntCC) -> IntCC {
+            cc.reverse()
+        }
+
+        #[inline]
+        fn intcc_inverse(&mut self, cc: &IntCC) -> IntCC {
+            cc.inverse()
+        }
+
+        #[inline]
+        fn floatcc_reverse(&mut self, cc: &FloatCC) -> FloatCC {
+            cc.reverse()
+        }
+
+        #[inline]
+        fn floatcc_inverse(&mut self, cc: &FloatCC) -> FloatCC {
+            cc.inverse()
+        }
+
         #[inline]
         fn unpack_value_array_2(&mut self, arr: &ValueArray2) -> (Value, Value) {
             let [a, b] = *arr;