[ClangImporter] Clean up adjustTypeForConcreteImport, part 2
(or part 4, depending on how you want to count)
Move the out-parameter logic into the switch over import hints (under
the OtherPointer case), and move the helper lambdas out into their own
functions. They're not called from anywhere else, but
adjustTypeForConcreteImport is long as it is.
Additionally, avoid early returns in the import hint switch; while
early returns are generally a good thing, having some cases
early-return and not others seems inconsistent. The post-switch logic
is pretty simple and easy to early-exit now.
No intended functionality change.
