Add implementation of editable strategy based on a link tree

[abravalheri]

Summary of changes

• Add implementation of editable strategy based on a link tree
  • This is the strict implementation.
  • Only files are linked, not directories.
    • This approach makes it possible to use harlinks when softlinks are not available (e.g. Windows)
    • It also guarantees files that would not be part of the final wheel are not available in the editable install.
• Add non-editable files to the produced wheel wheel (e.g. headers, scripts, data)

Closes

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d/.
  (See documentation for details)