refactor: use $$restProps API

- add ref prop for applicable components (#196)
- add slot to Content Switcher `Switch` component (#183)
- remove fillArray, css utilities

src/components/Notification/NotificationActionButton.svelte

@@ -1,20 +1,15 @@
 <script>
-  let className = undefined;
-  export { className as class };
-  export let style = undefined;
-
-  import { cx } from '../../lib';
-  import Button from '../Button';
+  import { Button } from "../Button";
 </script>
 
 <Button
   kind="ghost"
   size="small"
+  class="bx--inline-notification__action-button"
+  {...$$restProps}
   on:click
   on:mouseover
   on:mouseenter
-  on:mouseleave
-  class={cx('--inline-notification__action-button', className)}
-  {style}>
+  on:mouseleave>
   <slot />
 </Button>