fix(button): allow transition for the button focus overlay for all buttons (#12552)

Author: josephperrott

src/lib/button/button.scss

@@ -10,7 +10,7 @@
 
 .mat-button, .mat-icon-button {
   .mat-button-focus-overlay {
-    transition: none;
+
     opacity: 0;
   }
 }