REST API: Support the minProperties and maxProperties JSON Schema keywords.

Props yakimun.
Fixes #51023.


git-svn-id: https://develop.svn.wordpress.org/trunk@49053 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/rest-api/rest-test-controller.php

@@ -120,6 +120,8 @@ class WP_REST_Test_Controller extends WP_REST_Controller {
 							'type' => 'integer',
 						),
 					),
+					'minProperties'        => 1,
+					'maxProperties'        => 10,
 					'ignored_prop'         => 'ignored_prop',
 					'context'              => array( 'view' ),
 				),