Taxonomy: Filter the arguments passed into wp_dropdown_categories() in the Categories post edit metabox AJAX request output.

This commit fixes a bug that caused differing dropdown results between AJAX & non-AJAX output, when using the `post_edit_category_parent_dropdown_args` hook.

(That hook is documented inside of the `post_categories_meta_box()` function, introduced via r33682 and #33026.)

Props obiplabon, birgire.

Fixes #44343.

git-svn-id: https://develop.svn.wordpress.org/trunk@60492 602fd350-edb4-49c9-b593-d223f7449a82

Author: JJJ

src/wp-admin/includes/ajax-actions.php

@@ -690,18 +690,21 @@ function _wp_ajax_add_hierarchical_term() {
 		);
 	}
 
+	$parent_dropdown_args = array(
+		'taxonomy'         => $taxonomy->name,
+		'hide_empty'       => 0,
+		'name'             => 'new' . $taxonomy->name . '_parent',
+		'orderby'          => 'name',
+		'hierarchical'     => 1,
+		'show_option_none' => '— ' . $taxonomy->labels->parent_item . ' —',
+	);
+
+	/** This filter is documented in wp-admin/includes/meta-boxes.php */
+	$parent_dropdown_args = apply_filters( 'post_edit_category_parent_dropdown_args', $parent_dropdown_args );
+
 	ob_start();
 
-	wp_dropdown_categories(
-		array(
-			'taxonomy'         => $taxonomy->name,
-			'hide_empty'       => 0,
-			'name'             => 'new' . $taxonomy->name . '_parent',
-			'orderby'          => 'name',
-			'hierarchical'     => 1,
-			'show_option_none' => '— ' . $taxonomy->labels->parent_item . ' —',
-		)
-	);
+	wp_dropdown_categories( $parent_dropdown_args );
 
 	$sup = ob_get_clean();