fix(ripple): Apply will-change to surface rather than pseudo-elements (#1872)

This avoids a rendering regression in Safari where ripples/shade
expanded beyond the border-radius of the surface, and also generally
decreases the surface area affected by `will-change`.

Author: kfranqueiro

packages/mdc-ripple/_mixins.scss

@@ -28,6 +28,7 @@
   --mdc-ripple-fg-translate-start: 0;
 
   -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
+  will-change: transform, opacity;
 
   &::before,
   &::after {
@@ -36,7 +37,6 @@
     opacity: 0;
     pointer-events: none;
     content: "";
-    will-change: transform, opacity;
   }
 
   &::before {