Add pie artist - #32359

This PR is a follow up to #32320. It adds a Pie artist class and deprecates PieContainer. legend.py checks for a get_legend_handles method, so compound artists can expose their handles.

Previous state:

ax._children = [wedge1, wedge2, wedge3, text1, text2, text3],
ax.patches = [wedge1, wedge2, wedge3]
ax.texts = [text1, text2, text3]
ax.containers = []
pie_container1.wedges = [wedge1, wedge2, wedge3]

State after this PR:

ax._children = [pie1],
ax.patches = []
ax.texts = []
ax.containers = []
pie1.wedges = [wedge1, wedge2, wedge3]
pie1.texts = [text1, text2, text3]

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AI used to gain understanding of the existing code

• Use an expressive title, e.g. "Fix title font property precedence"
• New and changed code is tested
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• New features and API changes have release notes
• Documentation complies with general and docstring guidelines