Allow the ability to chain method return value for Access Policy marker path

[aamplugin]

Allow to use object's method to chain the path to marker's value. For example, lets say we have a global object $current_user that has a public method get_data. The method returns an array of key/value pairs, when you need to access "first_name" key.

The marker ${PHP_GLOBAL.current_user.get_data.first_name} will do the trick.