Move the common implementation of Axes.set_x/y/zscale to Axis.

[anntzer]

... together with an _axis_method_wrapper.

It may be worth trying to figure out later whether Axis._set_scale and
Axis._set_axes_scale need to have subtly different behaviors...

PR Summary

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• New features are documented, with examples if plot related.
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
• Documentation is sphinx and numpydoc compliant (the docs should build without error).

[oscargus]

The 3D-versions were not tested earlier. Would be nice to have a test that passes both before and after this PR.

[anntzer]

3D axes don't actually meaningfully support any scales other than linear, so I don't think we can really write meaningful tests there. Note that if anything this PR already improves the test coverage by getting rid of untested code (Axes3D.set_{x,y,z}scale).

[oscargus]

It improves the coverage for sure, I'm more worried about not changing behaviour. But after a more careful reading of the code, I can probably agree with you that it does the same thing as before.

[tacaswell]

The docs failure is understood as the sphinx-gallery reset issue, should not block.

The difference is that the autoscaling is now conditional, but I suspect that is OK.