Line2d window extents

[brunobeltran]

PR Summary

Goes on top of #17198. Only the "latest" commit of the two belongs to this PR.

WIP. Fix Line2D.get_window_extent. Supercedes the discussion in #16607. Still fixes #16606, but also accounts for line joins, caps, etc, and with much less code, thanks to updates to Path.

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

[github-actions]

Since this Pull Request has not been updated in 60 days, it has been marked "inactive." This does not mean that it will be closed, though it may be moved to a "Draft" state. This helps maintainers prioritize their reviewing efforts. You can pick the PR back up anytime - please ping us if you need a review or guidance to move the PR forward! If you do not plan on continuing the work, please let us know so that we can either find someone to take the PR over, or close it.