ENH: Add PolarAxes.get_rlim() and get_thetalim() for API symmetry

[tinezivic]

PR summary

PolarAxes has set_rlim() and set_thetalim() but no corresponding getters.
Added get_rlim() (delegates to get_ylim()) and get_thetalim() (delegates to get_xlim()).

Closes #31694

AI Disclosure

Used GitHub Copilot to understand the existing PolarAxes implementation. The fix and verification are my own.

PR checklist

PR checklist

• "closes [Bug]: PolarAxes missing get_rlim() and get_thetalim() getters #31694" is in the body of the PR description
• new and changed code is tested
• [N/A] Plotting related features are demonstrated in an example — N/A (new getter methods, no visual change)
• New Features and API Changes are noted with a directive and release note — added doc/release/next_whats_new/polar_get_rlim_thetalim.rst
• Documentation complies with general and docstring guidelines

[timhoffm]

Thanks, looks good except for small wording improvements.

[timhoffm]

Suggested change

	`~matplotlib.projections.polar.PolarAxes.set_thetalim`. Previously, calling
	these getters raised an ``AttributeError``; the workaround was to call the
	base-class ``get_ylim()`` / ``get_xlim()`` directly::
	`~matplotlib.projections.polar.PolarAxes.set_thetalim`. Previously, one
	had to use `.Axes.get_ylim`, `.Axes.get_xlim` as a workaround.
	::

Attribute error is implied when a method does not exist and is not worth mentioning.

Since you end with the previous behavior, don't :: at the end of it, because that renders
a : at the end of the sentence, which would falsely imply that the following example is related to the sentence.