Switch to Dart Sass and Sass modules.

[jgerigmeyer]

Todo:

• [x] upgrade node
• [x] upgrade deps
• [x] remove gulp
• [x] remove gulp-imagemin -- fixes #343
• [x] remove karma
• [x] remove node-sass (decide Sass implementation support) -- consider #239
• [x] upgrade Herman styles to module syntax
• [x] switch to Yarn2 for dev
• [x] detect PnP for custom importer -- fixes #350

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@ddaa9fc). Click here to learn what that means. The diff coverage is n/a.

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##             master      #348   +/-   ##
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  Coverage          ?   100.00%           
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  Files             ?        24           
  Lines             ?       997           
  Branches          ?       220           
==========================================
  Hits              ?       997           
  Misses            ?         0           
  Partials          ?         0           

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[jgerigmeyer]

I want Herman to less aggressively optimize user SVG icons.

[mirisuzanne]

@jgerigmeyer I've updated all the Sass to use modules - but I can't get the sass examples to compile correctly. Can you take a look?

[mirisuzanne]

I want Herman internals on Dart Sass

[jgerigmeyer]

@mirisuzanne Back to you.

[jgerigmeyer]

@mirisuzanne Next step is probably to merge this and do an RC release to test out on a few projects?