Move `AluEntities` enum into shared alucard.h header

[JoshSchreuder]

AluEntities currently lives in dra.h

There are cases in the stage/boss overlays which are using these entity IDs that could utilise this enum

For example:

• The bat echo check in CAT
• Doppelganger entity ID checks
  etc.

It would be worthwhile moving this out of dra.h into a more generalised header that can be included as required.