In some cases it's not possible to pass the current resource resolver done the call stack (as the methods do not provide a parameter to pass it). However, an implementation might want to use the request resource resolver.
We could generalize this and add a new method to the ResourceResolverFactory:
- ResourceResolver getCurrentResourceResolver().
This resolver is kept in a thread local stack.
Whenever RRF.getResourceResolver is called, the new resolver is put onto that stack.
When a RRF is closed, it's removed from the stack, even if it is not the top element.