This moves the EnumAttrCase and EnumAttr classes from Attribute.h/.cpp to a new EnumInfo.h/cpp and renames them to EnumCase and EnumInfo, respectively. This doesn't change any of the tablegen files or any user-facing aspects of the enum attribute generation system, just reorganizes code in order to make main PR (#132148) shorter.
Multi-Level Intermediate Representation
See https://mlir.llvm.org/ for more information.