REST API: Clean up argument and property types.

There's a couple of places where we were missing type notes for arguments, which mainly affects documentation.

Props jnylen0.
Fixes #38792.

Built from https://develop.svn.wordpress.org/trunk@39250


git-svn-id: http://core.svn.wordpress.org/trunk@39190 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/endpoints/class-wp-rest-comments-controller.php

@@ -1158,6 +1158,7 @@ class WP_REST_Comments_Controller extends WP_REST_Controller {
 							'description'     => __( 'HTML content for the object, transformed for display.' ),
 							'type'            => 'string',
 							'context'         => array( 'view', 'edit', 'embed' ),
+							'readonly'        => true,
 						),
 					),
 				),