Add a fixture project which runs with Xcode 14 for extension Kit extension

[mtj0928]

To track diffs related to extension kit extensions, we need to add a new fixture project which runs with Xcode 14 for extension Kit extension.

Because GitHub Actions don't support Xcode 14 yet, this issue should be handled after GitHub Actions start supporting it.

Related discussion. https://github.com/yonaskolb/XcodeGen/pull/1230#issuecomment-1189894302

[alessionossa]

I just discovered that GitHub Actions actually supported Xcode 14 betas during summer (https://github.com/actions/runner-images/issues/5702), however Xcode 14 is only available on macOS 12 (https://github.com/actions/runner-images/blob/main/images/macos/macos-12-Readme.md), while GitHub Actions for XcodeGen are still running on macOS 11.