Having bound types in TypeReprs causes trouble in several places
(mostly involving type-checking of generics), and doesn't really fit
with TypeReprs being a mostly syntactic construct. Eliminate some code
paths using getBoundType(), and make the others do the same thing for
getBoundDecl() and getBoundType(). As part of the latter, provide
TypeBase::getDirectlyReferencedTypeDecl() to more easily map from type
to the named declaration.
Swift SVN r32018
