PR Summary

angle must be passed as keyword argument from 3.6.

I'm working on tests for this and other anchored artists, but thought this should go on its own in 3.6 to not stall it with reviewing tests etc.

Tests are in #23863 (but not as important to get those into 3.6).

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• New features are documented, with examples if plot related.
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
• Documentation is sphinx and numpydoc compliant (the docs should build without error).