Replace usages of basename() with wp_basename() in order to support multibyte filenames

This is focused on the pieces of code that touch media files and the tests that support them. `basename` isn't multibyte compatible out of the box. See http://php.net/basename and https://bugs.php.net/bug.php?id=62119.

See #43170.
Props Viper007Bond.


git-svn-id: https://develop.svn.wordpress.org/trunk@44785 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/customize/class-wp-customize-media-control.php

@@ -92,7 +92,7 @@ class WP_Customize_Media_Control extends WP_Customize_Control {
 					'url'   => $this->setting->default,
 					'type'  => $type,
 					'icon'  => wp_mime_type_icon( $type ),
-					'title' => basename( $this->setting->default ),
+					'title' => wp_basename( $this->setting->default ),
 				);
 
 				if ( 'image' === $type ) {