Fix centre square rectangle selector part 1

[ericpre]

@dstansby, as mentioned in #20839 (comment), this is the first part of #20839.

PR Summary

• Fix centre and square state of rectangle selector in interactive mode. These states were working only when creating the selector.
• Fix name coordinate handle: N and S were swapped.
• Rebased on latest main branch.

import matplotlib.pyplot as plt
from matplotlib.widgets import RectangleSelector
import numpy as np

values = np.arange(0, 100)

fig = plt.figure()
ax = fig.add_subplot()
ax.plot(values, values)

selector = RectangleSelector(ax, print, interactive=True, drag_from_anywhere=True)

# change the size of selector interactively

PR Checklist

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (run flake8 on changed files to check).
• [n/a] New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• Conforms to Matplotlib style conventions (install flake8-docstrings and run flake8 --docstring-convention=all).
• [n/a] New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• [n/a] API changes documented in doc/api/next_api_changes/ (follow instructions in README.

[dstansby]

Looks good overall - I've left a few suggestions and questions.

[ericpre]

Thanks, all comments should have been addressed!

[dstansby]

Thanks - all looks good to me!

[dstansby]

I think this is a bugfix, so going to milestone to 3.5.x - second reviewer feel free to correct me on this.

[ericpre]

Thanks @dstansby, once the second review is done and this PR is merged, I will see how to split the rest of #20839.

[timhoffm]

@ericpre Since you plan a followup PR, the comment on using tuples can be addressed therein. I'll merge as is to enable you continuing with that PR.

[timhoffm]

I would use tuples instead of lists for coordinates.