docs: correct the suggested type for custom events without detail (Svelte 4) (#15763)

* docs: correct the suggested type for custom events without detail

* docs: generate fixed types for the Svelte 4 event dispatcher

.changeset/fifty-buckets-return.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+correct the suggested type for custom events without detail

packages/svelte/src/index-client.js

@@ -114,7 +114,7 @@ function create_custom_event(type, detail, { bubbles = false, cancelable = false
  * The event dispatcher can be typed to narrow the allowed event names and the type of the `detail` argument:
  * ```ts
  * const dispatch = createEventDispatcher<{
- *  loaded: never; // does not take a detail argument
+ *  loaded: null; // does not take a detail argument
  *  change: string; // takes a detail argument of type string, which is required
  *  optional: number | null; // takes an optional detail argument of type number
  * }>();

packages/svelte/types/index.d.ts

@@ -381,7 +381,7 @@ declare module 'svelte' {
 	 * The event dispatcher can be typed to narrow the allowed event names and the type of the `detail` argument:
 	 * ```ts
 	 * const dispatch = createEventDispatcher<{
-	 *  loaded: never; // does not take a detail argument
+	 *  loaded: null; // does not take a detail argument
 	 *  change: string; // takes a detail argument of type string, which is required
 	 *  optional: number | null; // takes an optional detail argument of type number
 	 * }>();