Resolve "Add Xcode Button in UI"

What does this MR do?

Adds a "Open in Xcode" button if the repository is of an xcode project.

Are there points in the code the reviewer needs to double check?

This is currently patched in production for 10.8.3.

Hopefully this will get in before RC2.

Why was this MR needed?

It has finally been announced on the WWDC stage.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer (Reviewed at: https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2389)
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer (Reviewed at: https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2389)
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered

What are the relevant issue numbers?

Closes #45820 (closed)