style: Make LengthPercentage not copy.

This is needed to support min() / max() / clamp(), etc.

Differential Revision: https://phabricator.services.mozilla.com/D57249

components/style/values/animated/transform.rs

@@ -1373,7 +1373,11 @@ impl ComputedTranslate {
                 LengthPercentage::zero(),
                 Length::zero(),
             ),
-            Translate::Translate(tx, ty, tz) => (tx, ty, tz),
+            Translate::Translate(ref tx, ref ty, ref tz) => (
+                tx.clone(),
+                ty.clone(),
+                tz.clone(),
+            ),
         }
     }
 }