This PR makes the error when cm-super is not installed (and
rcParams["text.latex.unicode"] = True, which is now the default) be

! LaTeX Error: File `type1ec.sty' not found.Type X to quit or <RETURN> to proceed,or enter new name. (Default extension: sty)Enter file name:! Emergency stop.<read *>l.5 \usepackage               {type1ec}^^MNo pages of output.

(or, if using miktex, miktex will prompt for installing cm-super).

Closes#14146, I think.

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code isFlake 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