This enables the editor directory to be linted, and fixes the remaining issues raised by ESLint. Various rules were fixed here including, no-shadow, no-undef, no-unused-vars and others.
I've generally gone conservative, disabling rules where it doesn't make sense to fix them (e.g. sometimes suggests use-services for tests, but it is only used once, or within a Chrome script).
Depends on D5585
Differential Revision: https://phabricator.services.mozilla.com/D5587
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extra : moz-landing-system : lando
Also block-disables no-multi-spaces for test_resizers_resizing_elements.html
Differential Revision: https://phabricator.services.mozilla.com/D5584
--HG--
extra : moz-landing-system : lando