Fix #13963.

This commit fixes several things:

1. RuntimeRep arg suppression was overeager for *visibly*-quantified
RuntimeReps, which should remain.

2. The choice of whether to used a Named TyConBinder or an anonymous
was sometimes wrong. Now, we do an extra little pass right before
constructing the tycon to fix these.

3. TyCons that normally cannot appear unsaturated can appear unsaturated
in :kind. But this fact was not propagated into the type checker.
It now is.