Pure documentation change: The link to the performance comparison in the "sparse solvers" section showed the same image from the "dense solvers" section.

The plot titles are a bit cropped, but I think it's still more informative to show the data that is referenced in the text on the page.

(If understood the guidelines for contributing correctly, none of the points on the checklist below apply here.)

Checklist

• Appropriate tests were added
• Any code changes were done in a way that does not break public API
• All documentation related to code changes were updated
• The new code follows the
  contributor guidelines, in particular the SciML Style Guide and
  COLPRAC.
• Any new documentation only uses public API