[turbofan] Avoid unnecessary tagging of floating point values.

Replace ChangeFloat64ToTagged(ChangeTaggedToFloat64(x)) with x in the
SimplifiedOperatorReducer.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1883023003

Cr-Commit-Position: refs/heads/master@{#35488}

src/compiler/simplified-operator-reducer.cc

@@ -47,6 +47,7 @@ Reduction SimplifiedOperatorReducer::Reduce(Node* node) {
     case IrOpcode::kChangeFloat64ToTagged: {
       Float64Matcher m(node->InputAt(0));
       if (m.HasValue()) return ReplaceNumber(m.Value());
+      if (m.IsChangeTaggedToFloat64()) return Replace(m.node()->InputAt(0));
       break;
     }
     case IrOpcode::kChangeInt32ToTagged: {