Script Loader: Use a global variable in wp_script_modules().

This brings the function more in line with its related `wp_scripts()` and `wp_styles()` functions and makes it easier to reset the class instance in tests.

Props westonruter, luisherranz.
See #56313.

git-svn-id: https://develop.svn.wordpress.org/trunk@57503 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/script-modules.php

@@ -14,17 +14,20 @@
  * This function provides access to the WP_Script_Modules instance, creating one
  * if it doesn't exist yet.
  *
+ * @global WP_Script_Modules $wp_script_modules
+ *
  * @since 6.5.0
  *
  * @return WP_Script_Modules The main WP_Script_Modules instance.
  */
 function wp_script_modules(): WP_Script_Modules {
-	static $instance = null;
-	if ( is_null( $instance ) ) {
-		$instance = new WP_Script_Modules();
-		$instance->add_hooks();
+	global $wp_script_modules;
+
+	if ( ! ( $wp_script_modules instanceof WP_Script_Modules ) ) {
+		$wp_script_modules = new WP_Script_Modules();
 	}
-	return $instance;
+
+	return $wp_script_modules;
 }
 
 /**

src/wp-settings.php

@@ -378,6 +378,8 @@
 require ABSPATH . WPINC . '/script-modules.php';
 require ABSPATH . WPINC . '/interactivity-api.php';
 
+wp_script_modules()->add_hooks();
+
 $GLOBALS['wp_embed'] = new WP_Embed();
 
 /**