swift234

Whether a canonical type has been constructed for a given type is not
a reliable way to track whether a particular type has been
validated. Instead, add some bits to the type to indicate which stage
of checking it has received. I hate it, but it works and I don't know
of a better way to ensure that types get validated. This subsystem
will need to get rearchitected at some point (ugh).

Reduce the number of places where we build new BoundGenericTypes,
since they need to be validated fully to get substitutions, and then
introduces a number of validateTypeSimple() calls to validate types in
places where we know the validation will succeed, but we need that
information regardless.


Swift SVN r2681