Docs: Standardise and correct documentation relating to parameters which accept plugin names.

See #42505


git-svn-id: https://develop.svn.wordpress.org/trunk@42787 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/load.php

@@ -653,14 +653,14 @@ function wp_get_mu_plugins() {
  *
  * While upgrading or installing WordPress, no plugins are returned.
  *
- * The default directory is wp-content/plugins. To change the default
+ * The default directory is `wp-content/plugins`. To change the default
  * directory manually, define `WP_PLUGIN_DIR` and `WP_PLUGIN_URL`
- * in wp-config.php.
+ * in `wp-config.php`.
  *
  * @since 3.0.0
  * @access private
  *
- * @return array Files.
+ * @return string[] $plugin_file Array of paths to plugin files relative to the plugins directory.
  */
 function wp_get_active_and_valid_plugins() {
 	$plugins        = array();