fix plotting analytic time series

[ranocha]

Fixes SciML/OrdinaryDiffEq.jl#2162

The changes of this part of the code were introduced in https://github.com/SciML/SciMLBase.jl/pull/572/files

I also added some real (smoke) tests for this, including loading Plots.jl and generating some plots (maybe unicodeplots?).

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

Additional context

It would be nice to get a new release including this fix.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 29.88%. Comparing base (3746cda) to head (f84c40e).

Files	Patch %	Lines
src/solutions/solution_interface.jl	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #655      +/-   ##
==========================================
- Coverage   38.43%   29.88%   -8.56%     
==========================================
  Files          55       55              
  Lines        4298     4290       -8     
==========================================
- Hits         1652     1282     -370     
- Misses       2646     3008     +362     

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[ranocha]

Thanks! Could we maybe get a new release of SciMLBase.jl soon to fix our CI issues, please?