refactor(button): some missing changes from spectrum-two rebase

Some changes around the pending state were missing after rebasing with
the latest spectrum-two branch. Manual resolution of differences.

components/button/index.css

@@ -915,7 +915,16 @@ governing permissions and limitations under the License.
 
     .spectrum-Icon,
     .spectrum-Button-label {
-      display: none;
+      visibility: hidden;
+      opacity: 0%;
+      transition: opacity var(--mod-button-animation-duration, var(--spectrum-button-animation-duration, 130ms)) ease-in-out,
+                  visibility 0ms linear var(--mod-button-animation-duration, var(--spectrum-button-animation-duration, 130ms));
+    }
+
+    .spectrum-ProgressCircle {
+      visibility: visible;
+      opacity: 100%;
+      transition: opacity var(--mod-button-animation-duration, var(--spectrum-button-animation-duration, 130ms)) ease-in-out;
     }
   }
 }