PR Summary

Turned out to be very hard to rebase #13034 so I've cherry-picked the relevant commits and fixed the style comments. Edit: realized that #13034 was heavily based on #10688 so I've added @magedhennawy as coauthor as well.

Closes #13034
Fixes #8236

A problem here is when an annotation is added, but no arrow is given, it will break. Not sure what is expected to happen in this case. Providing a better exception is easy, something like "An annotation must have an arrow if a label is provided" while creating the annotation, but maybe better to get an empty patch in the legend?

Adding an annotation with a label, but no arrow will lead to an empty patch. In #13034 it was not handled (gave an error).

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).