Native bindings and AnimInstanceProxy usage

[Schmurf]

Hello!

Since the project is aiming for performance:

• On State Entry/Exit/Transitions bindings could be done in c++ using corresponding AddNativeXBinding() and avoid going through the BP VM.
  Would a PR moving thoses function to C++ be accepted?

• Lot of nodes or transition result could also be done in the AnimInstanceProxy to avoid blueprint usage.

• I'm pretty sure the entire Layering Anim Graph Layer could be done inside a c++ node in a proxy and avoid much BP overhead.

Is it not used for AnimGraph Readability purpose?