[cxx-interop] Always import the lifetime annotations
Importing these annotations were behind the LifetimeDependence
experimental flag. However, this feature flag is intended to guard the
use of @lifetime annotations on the Swift side and lifetime inference.
The checking of imported lifetime contracts should work even when this
flag is off. Removing the flag from the importer caused some fallout.
This was mostly due to calling getInterfaceType functions before the
import of some Swift declarations were fully done so the code was
slightly improved to make decisions only based on the C++ types.
There was also a crash when on-member functions imported as methods into
Swift. That is worked around in this PR.
There is one last feature check that we cannot remove yet, we generate
@lifetime annotations in the SwiftifyImport macro.
