Track Drupal 8 Javascript changes

As Drupal 8's Javascript is continuously changing, we need to keep up with those changes. I'll try to keep a list of changes here that affect TestSwarm.

Changes committed to Drupal 8

• JavaScript settings moved from Drupal.settings to global drupalSettings variable.
  • Issue: #1760548: Remove dependency on jQuery and drupal.js for JS settings
  • Change notification: JavaScript settings moved from Drupal.settings to global drupalSettings variable
• drupal_json_output is removed in favor of Symfony\Component\HttpFoundation\JsonResponse
  • Issue: #1619446: All autocomplete and drupal_json_output() responses are broken (returning Ajax instead of JSON)
  • Change notification: drupal_json_output is removed in favor of Symfony\Component\HttpFoundation\JsonResponse
• All collapsible fieldsets have been replaced with HTML5 details elements
  • Issue: #1168246: Freedom For Fieldsets! Long Live The DETAILS.
  • Change notification: All collapsible fieldsets have been replaced with HTML5 details elements

Issues to keep an eye on

#1852104: #type details: Remove #collapsible property
#1839158: Replace collapse.js with a proper polyfill for <details>
#1856178: '#group' Form API property only works with <details> elements
#1858600: "Filter log messages" details on Recent log messages page applies bogus floats