There's a mention of this in the "Issues" document here:
https://github.com/apple/swift-corelibs-foundation/blob/master/Docs/Issues.md#known-issues
That makes it sound like this isn't meant to be a long term limitation:
> In order to translate between these types, we have temporarily added a
>
Hey all,
I was working on integrating a project with corelibs-xctest and I noticed that
it doesn't currently support building with swiftpm and instead provides
`.xcodeproj` which generates a `.framework`. Is there any future plan to also
include a `Package.swift` so that user's could build it
