REST API: Add more specific error codes for schema validation.

Previously, the majority of JSON Schema validation errors returned a generic `rest_invalid_param` error code. In preparation for #46191, where the underlying validation error code will be exposed, this commit adds specific error codes for each failure scenario.

Fixes #52317.


git-svn-id: https://develop.svn.wordpress.org/trunk@50007 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -164,7 +164,7 @@ class WP_Test_REST_Controller extends WP_Test_REST_TestCase {
 		);
 
 		$this->assertErrorResponse(
-			'rest_invalid_param',
+			'rest_not_in_enum',
 			rest_validate_request_arg( 'd', $this->request, 'someenum' )
 		);
 	}