Refactor prop types to omit redundant null for null | HTMLElement types (#998)

* refactor: omit redundant `null` prop type for HTMLElements

* yarn build:lib

* test: assert updated element prop types

src/DataTable/ToolbarSearch.svelte

@@ -21,7 +21,7 @@
 
   /**
    * Obtain a reference to the input HTML element
-   * @type {null | HTMLInputElement}
+   * @type {HTMLInputElement}
    */
   export let ref = null;