swift234

Revise our AST to represent the self argument of a non-mutating protocol method
as passing self by value, not by inout.  This is the correct representation at
the AST level, and we now lower self references as the new @in_guaranteed
parameter convention.  This allows SIL clients (like DI) to know that a nonmutating
protocol method does not mutate the pointee passed into the method.

This fixes:
<rdar://problem/19215313> let properties don't work with protocol method dispatch
<rdar://problem/15821762> Self argument of generic curried nonmutating instance methods is inout



Swift SVN r23864