feat(minor): [sc-28167] move Transferable.swift protocols to DistributedABI module

[tayloraswift]

Description

we can use @_exported to make this change transparent to clients

this module is set to -enable-library-evolution when built by itself, but this module only contains protocols so it shouldn’t affect users

even if we don’t end up vending DistributedABI as an xcframework, this would still be a beneficial architectural change in its own right

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

Minimal checklist:

• I have performed a self-review of my own code
• I have added DocC code-level documentation for any public interfaces exported by the package
• I have added unit and/or integration tests that prove my fix is effective or that my feature works

[tayloraswift]

lint failures almost certainly predate PR

[mr-swifter]

Looking to history it was originally split similar to this, but then we merged this back for simplicity: https://github.com/ordo-one/package-distributed-system-conformance

One question although. If I do some 3rd party application and link distributed system (statically). I guess this change will change the way how I ship my app. Since before I get self sufficient binary, but now this dependency is built as separate library and should be shipped together with my app. Feels like major break. Do I miss something?

[tayloraswift]

i believe (but am not 100% sure) that -enable-library-evolution is orthogonal to library type .dynamic, and will not by itself change how clients that depend on DistributedSystem are built