REST API: add `JsonSerializable()` compatibility interface for PHP <5.4 to `compat.php`

Props rmmcue.
See #33982.

Built from https://develop.svn.wordpress.org/trunk@34845


git-svn-id: http://core.svn.wordpress.org/trunk@34810 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/compat.php

@@ -316,3 +316,19 @@ if ( ! function_exists( 'json_last_error_msg' ) ) :
 		}
 	}
 endif;
+
+if ( ! interface_exists( 'JsonSerializable' ) ) {
+	define( 'WP_JSON_SERIALIZE_COMPATIBLE', true );
+	/**
+	 * JsonSerializable interface.
+	 *
+	 * Compatibility shim for PHP <5.4
+	 *
+     * @link http://php.net/jsonserializable
+	 *
+	 * @since 4.4.0
+	 */
+	interface JsonSerializable {
+		public function jsonSerialize();
+	}
+}

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.4-alpha-34844';
+$wp_version = '4.4-alpha-34845';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.