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/ListItem/ListItem.svelte

@@ -1,11 +1,9 @@
-<script>
-  let className = undefined;
-  export { className as class };
-  export let style = undefined;
-
-  import { cx } from '../../lib';
-</script>
-
-<li on:click on:mouseover on:mouseenter on:mouseleave class={cx('--list__item', className)} {style}>
+<li
+  class:bx--list__item={true}
+  {...$$restProps}
+  on:click
+  on:mouseover
+  on:mouseenter
+  on:mouseleave>
   <slot />
 </li>

src/components/ListItem/index.js

@@ -1,3 +1 @@
-import ListItem from './ListItem.svelte';
-
-export default ListItem;
+export { default as ListItem } from "./ListItem.svelte";