FIX: don't round image sizes to pixel if meant to be unsampled

[jklymak]

Closes #8981

PR Summary

For images we do some pixel rounding, but if we are doing unsampled images (eg imshow(..., interpolation='none')) and saving to a backend that allows rasters (svg, pdf), then we don't want to do the pixel rounding - that just makes the image sizes fractionally too large when that isn't needed at all if we don't resample.

All the test images that changed just model my a pixel, and all have imshow(..., interpolation='none').

Old

New

code

import numpy as np
import matplotlib.pyplot as plt

fig, ax = plt.subplots()
ax.plot([0, 0, 1, 1, 0], [0, 1, 1, 0, 0], color='r', lw=0.1)
np.random.seed(19680801)
ax.imshow(np.random.randn(16, 16), cmap='Blues', extent=(0, 1, 0, 1),
            interpolation='none', vmin=-1,vmax=1)
ax.set_xlim(-0.1, 1+0.1)
ax.set_ylim(-0.1, 1+0.1)

PR Checklist

Documentation and Tests

• Has pytest style unit tests (and pytest passes)
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• New plotting related features are documented with examples.

Release Notes

• New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst

[oscargus]

I haven't checked, but maybe make sure that all of the now modified images have style='mpl20'?

[jklymak]

I think for review send posterity it probably makes sense to leave the images in the style they are already in? It's pretty easy to see they are only trivially changed whereas if we changed the colormaps they would change a lot. I think the style changes are minimal for these ones anyway - just colormaps for instance. While I appreciate there are those who hate jet, it's probably OK for testing 😀

[oscargus]

Yes, it for sure make sense during the review to use the same style. Was more thinking of the overall goal from #24716

[jklymak]

Hopefully it will be moot when @tacaswell finishes his procedure for keeping track of image changes

[QuLogic]

@meeseeksdev backport to v3.7.x