swift234

Create protocol conformances and then, separately, fill in the witnesses.

This is a structural baby step toward lazily filling in protocol
conformances. We always build a ProtocolConformance, then mark it
either "complete" (when it's well-formed) or "invalid" (when it's
ill-formed). At present, the only benefit to this is that it slows
diagnostic cascades from invalid conformances.


Swift SVN r11492