swift234

Form TypeExprs for non-specialized unqualified declrefs that refer to types... like "Int".
Building on previous work, this allows us to properly handle things like Int?() and Int[]().

Of course doing this exposed that TypeExpr was not correct in lots of ways, so this also:
 - Revamps TypeExpr processing to carry a decl in the TypeLoc instead of 
   carrying a Type.  This allows us to correctly handle more complex generics case.  
 - Enhances CSGen to properly open generic types so we can infer generic type parameters from
   context.


Swift SVN r17019