Since we rarely touch this code, I took the liberty of changing this to a JS class
and fix the contrast ratio calculations to actually conform to the WCAG spec,
instead of using arbitrary constants.
I changed the `isBright` getter to `useBrightText`, because that is more apt;
we're usually looking for an answer to 'should I use white text on this background?',
instead of looking for an arbitrary threshold to classify a color as being bright.
I updated the tests to cover more of this and clarified the assertion messages as
well.
Differential Revision: https://phabricator.services.mozilla.com/D26097
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extra : moz-landing-system : lando
Automatic changes by ESLint, except for manual corrections for .xml files.
Differential Revision: https://phabricator.services.mozilla.com/D4439
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extra : moz-landing-system : lando
