feat: Add SPM sample

[github-actions]

Note

The pull request "feat: Add SPM sample" was created by @noahsmartin but did not reference an issue. Therefore this issue was created for better visibility in external tools like Linear.

This adds a sample app that builds natively with SPM. I don't want to call this GA yet, but once we merge this it will be possible for anyone to build with SPM and I would update the docs to call it a pre-release. With a future major version we can update all the public API to be in Swift and then call it GA

#skip-changelog

[linear]

COCOA-948