swift234

Carve out a new TypeCheckAttr.cpp file, and sketch out a new structure for doing
attribute checking on a per attribute basis.  It makes a lot more sense for a 
given attribute to think about all of the decl kinds it may or may not apply to
rather than all decl kinds thinking about the cross products of attributes they 
may apply to.

Start by adding a new check to reject @final in structs and enums.


Swift SVN r15925