[SE-NNNN] Package Manager Mixed Language Target Support

[ncooke3]

This is a formal proposal for adding mixed language target support to Swift Package Manager.

Relevant Links:

• Implementation: Add support for targets with mixed language sources swift-package-manager#5919
• Pitches: Pre-Pitch, Pitch

[tomerd]

thank you @ncooke3 for the proposal and implementation. we discussed the proposal on the core team meeting this week and there is a consensus this is an important proposal which requires the attention of C++ and language workgroups members. given other proposals in the language space and the general schedule for these workgroups, we want to give these reviewers enough time to adequately review this proposal. we believe we can come back to it around march, and run it then. feel free to reach out via the forums if further discussion is in place.