[Bug]: ContourSet.antialiased attribute not present

[rcomer]

Bug summary

The new ContourSet does not have an antialiased attribute. This causes failures in Iris, which checks the attribute.

Code for reproduction

import matplotlib.pyplot as plt

cs = plt.contour([[0, 1], [1, 2]], antialiased=True)
cs.antialiased

Actual outcome

Traceback (most recent call last):
  File "/contour_antialiased.py", line 4, in <module>
    cs.antialiased
AttributeError: 'QuadContourSet' object has no attribute 'antialiased'. Did you mean: '_antialiaseds'?

Expected outcome

With v3.7.1, I can access this attribute.

Additional information

Marking as release critical, as this is a regression.

Operating system

RHEL7

Matplotlib Version

main

Matplotlib Backend

QtAgg

Python version

3.11.4

Jupyter version

N/A

Installation

git checkout

[rcomer]

I'm pretty sure Iris could do without this attribute, as it could just use the return value of setdefault here. I have verified locally that Iris's tests pass with that change. But a deprecation period on the attribute would be useful.