REST API: Support the patternProperties JSON Schema keyword.

Props yakimun.
Fixes #51024.


git-svn-id: https://develop.svn.wordpress.org/trunk@49082 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -121,6 +121,11 @@ class WP_REST_Test_Controller extends WP_REST_Controller {
 							'type' => 'integer',
 						),
 					),
+					'patternProperties'    => array(
+						'[0-9]' => array(
+							'type' => 'string',
+						),
+					),
 					'minProperties'        => 1,
 					'maxProperties'        => 10,
 					'ignored_prop'         => 'ignored_prop',