docs: Switch typing of Action<Parameter> from null to undefined in 12-use.md (#14798)

* Update 12-use.md -

* Remove unecessary line in Action typing example

* drive-by formatting fix

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

documentation/docs/03-template-syntax/12-use.md

@@ -50,17 +50,16 @@ The `Action` interface receives three optional type arguments — a node type (w
 ```svelte
 <!--- file: App.svelte --->
 <script>
-	import { on } from 'svelte/events';
-
 	/**
 	 * @type {import('svelte/action').Action<
 	 * 	HTMLDivElement,
-	 * 	null,
+	 * 	undefined,
 	 * 	{
 	 * 		onswiperight: (e: CustomEvent) => void;
 	 * 		onswipeleft: (e: CustomEvent) => void;
 	 * 		// ...
-	 * }>}
+	 * 	}
+	 * >}
 	 */
 	function gestures(node) {
 		$effect(() => {