swift234

[CodeCompletion] Refactor archetype transform to avoid using recursion. rdar://27615558

We have a radar (rdar://27615558) complaining the exiting recursive calls in type transform
of code completion hangs. This patch refactor the existing code to avoid using
recursion. From existing tests' perspective, this is NFC. I am not able to contrive the
test case that leads to the hang, neither is given by the radar.