The APIJSON tests used the default module cache and generated different
modules under the same name. This lead some tests to load a different
module than intended. This was made more easily detectable with the lock
on the swiftmodules instead of the swiftinterfaces.
Add a new swift-frontend driver option that extract APIs in the swift
module and print in JSON format. This is to allow tooling to understand
and process swift APIs without the need to be a swift compiler or
understand swift module/AST.
