Make JS utilities less intrusive

[anselmbradford]

Our JS utility CSS classes force display: block, which can break elements that have flexbox set, for example. @wpears suggested this refactoring that uses scripting media (see support https://caniuse.com/?search=css-media-scripting)

@media (scripting: none) {
  .u-js-only {
    display: none !important;
  }
}

@media (scripting: enabled) {
  .u-hide-if-js{
    display: none !important;
  }
}

@sonnakim for awareness