REST API: Add additional fields to the themes controller.

When the themes controller was introduced it only returned a theme's supported features. This adds the majority of a theme's header information to the response.

Props ockham, spacedmonkey.
Fixes #49906.


git-svn-id: https://develop.svn.wordpress.org/trunk@47921 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/theme/themeDir.php

@@ -163,6 +163,7 @@ class Tests_Theme_ThemeDir extends WP_UnitTestCase {
 			'Theme with Spaces in the Directory',
 			'Internationalized Theme',
 			'camelCase',
+			'REST Theme',
 		);
 
 		sort( $theme_names );