• [notes section required to get data note injection right] has been
  obsoleted by DATA_PARAMETER_PLACEHOLDER; get rid of them.
• loglog, semilogx, semilogy are thin wrappers around plot; it seems
  fine to not document data there and leave it implicitly part of
  **kwargs: all parameters supported by plot. Then "Other Parameters"
  only contains**kwargs whose description is quite short, so it can
  just be lifted into the main Parameters section rather than requiring
  a separate section just for itself.
• Likewise forstep, but that method actually explicitly listsdata
  in its signature, so just move its (already existing) description down
  to its correct position.

This change was motivated by the fact that DATA_PARAMETER_PLACEHOLDER is
not correctly handled for these simple plot() wrappers; because they all
operate without going through _preprocess_data(), fixing them would also
require their own ad-hoc solution anyways. (#21135)

PR Summary

PR Checklist

• Has pytest style unit tests (andpytest passes).
• IsFlake 8 compliant (runflake8 on changed files to check).
• New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs shouldbuild without error).
• Conforms to Matplotlib style conventions (installflake8-docstrings and runflake8 --docstring-convention=all).
• New features have an entry indoc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented indoc/api/next_api_changes/ (follow instructions in README.rst there).