[compiler] MoveOptimization should only merge identical moves

MoveOptimization merged moves based on canonicalized
`InstructionOperand`s, which ignores word representations. This can
lead to issues with tagged and Word32 representations, which could
happen on the same value and are not interchangeable.
This CL removes the canonicalization, only merging completely identical
moves.

Bug: chromium:1468148
Change-Id: I47e533616f7b11be6862e3f06d04636239d536ac
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4733512
Auto-Submit: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/main@{#89272}

src/compiler/backend/move-optimizer.cc

@@ -19,10 +19,10 @@ struct MoveKey {
 
 struct MoveKeyCompare {
   bool operator()(const MoveKey& a, const MoveKey& b) const {
-    if (a.source.EqualsCanonicalized(b.source)) {
-      return a.destination.CompareCanonicalized(b.destination);
+    if (a.source != b.source) {
+      return a.source.Compare(b.source);
     }
-    return a.source.CompareCanonicalized(b.source);
+    return a.destination.Compare(b.destination);
   }
 };