PR Summary

Not really an argument for the PR, but note that (unusually), the contextmanager form is much faster:

In [5]: %timeit _orig = plt.rcParams.copy(); pass; plt.rcParams.update(_orig)
633 µs ± 3.87 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

In [6]: %timeit with plt.rc_context(): pass
14.6 µs ± 578 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

I believe (haven't profiled it) that's because plt.rc_context() intentionally doesn't revalidate the original rcs when restoring them.

PR Checklist

• Has Pytest style unit tests
• Code is PEP 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way