Add eventStream signature to ResponseFactory contract (laravel#56306)

Adds `eventStream` to `Illuminate\Contracts\Routing\ResponseFactory` in order to add type support for this method, aligning this with the same behavior that we have for `stream` of which `eventStream` is a convenient wrapper.

Author: csfh

src/Illuminate/Contracts/Routing/ResponseFactory.php

@@ -57,6 +57,16 @@ public function json($data = [], $status = 200, array $headers = [], $options =
      */
     public function jsonp($callback, $data = [], $status = 200, array $headers = [], $options = 0);
 
+    /**
+     * Create a new event stream response.
+     *
+     * @param  \Closure  $callback
+     * @param  array  $headers
+     * @param  \Illuminate\Http\StreamedEvent|string|null  $endStreamWith
+     * @return \Symfony\Component\HttpFoundation\StreamedResponse
+     */
+    public function eventStream($callback, array $headers = [], $endStreamWith = '</stream>');
+
     /**
      * Create a new streamed response instance.
      *