MemoryReservation should expose MemoryConsumer #7999
Description
Is your feature request related to a problem or challenge?
At the moment it looks impossible to implement new MemoryManager outside of datafusion crate as it is impossible to retrieve MemoryConsumer. MemoryConsumer is needed to check if consumer can_spill
Describe the solution you'd like
A new method pub fn consumer(&self) -> &MemoryConsumer to be implemented in MemoryReservation exposing reference to the MemoryConsumer
Describe alternatives you've considered
I have considered exposing Arc<SharedRegistration> instead of MemoryConsumer but it does not have any usefull additional information
Additional context
Relates to #7858