Sync dash pattern change for matplotlib >= 3.6.0

[FriedrichFroebel]

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This fixes #580, which has been broken since the matplotlib change in https://github.com/matplotlib/matplotlib/pull/21050/commits/9c0fa9ed83a825eb34ae8d44ba1b4123145f8422 for version 3.6.0.

This PR is similar to #571, but has two differences:

• It keeps the backwards-compatibility for older matplotlib versions.
• It uses the unscaled dash patterns as indicated by the old _us_ variable name, while #571 apparently switched to the scaled one.