swift234

Introduce patterns for self arguments to ctors and dtors, making them uniform
with FuncDecls.  This allows us to eliminate special case code for handling
self in various parts of the compiler.

This also improves loc info (debug info and AST info) because 'self' now
has a location instead of being invalid.

I also took the opportunity to factor a bunch of places creating self decls
to use similar patterns and less copy and paste code.



Swift SVN r13196