Add Widget Extension support to AppClips

[pepicrft]

Short description 📝

Tuist doesn't support defining widget extensions for app clips. This PR adds support for it.

Contributor checklist ✅

• The code has been linted using run mise run lint:fix
• The change is tested via unit testing or acceptance testing, or both
• The title of the PR is formulated in a way that is usable as a changelog entry
• In case the PR introduces changes that affect users, the documentation has been updated

Reviewer checklist ✅

• The code architecture and patterns are consistent with the rest of the codebase
• Reviewer has checked that, if needed, the PR includes the label changelog:added, changelog:fixed, or changelog:changed, and the title is usable as a changelog entry

[danieleformichelli]

Can't we extend the ios_app_with_appclip instead of creating a brand new fixture?

[pepicrft]

Can't we extend the ios_app_with_appclip instead of creating a brand new fixture?

Yes! I'll do that instead.