Bundled Themes: Make Twenty Twenty the new default theme.

After being imported in [46271], Twenty Twenty can now be set as the default theme in WordPress.

See #48110.
Props desrosj, ocean90.

git-svn-id: https://develop.svn.wordpress.org/trunk@46278 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-theme.php

@@ -54,6 +54,7 @@ final class WP_Theme implements ArrayAccess {
 		'twentysixteen'   => 'Twenty Sixteen',
 		'twentyseventeen' => 'Twenty Seventeen',
 		'twentynineteen'  => 'Twenty Nineteen',
+		'twentytwenty'    => 'Twenty Twenty',
 	);
 
 	/**