Better handling of stylesheet links that have `disabled` and/or `media`

The issue:

• The browser will not load stylesheets from links with the disabled attribute.
• The polyfill currently will load such links, and if any changes are applied, replace them with new links without disabled
• Even if the polyfill is modified to preserve disabled, it might not be desirable to fetch the resource in the first place. (fixed in #262)
• The same might be said for links with a media attribute when the media query is not currently satisfied.

My rough idea to address the issue is basically this:

• For any stylesheet link that the polyfill would process:
  • Check if it is disabled. If so, add a MutationObserver with { attributeFilter: ['disabled'] } that will handle processing the stylesheet if it were to become no longer disabled.
  • Check if it has media, and if so, create a MediaQueryList. If the media query list does not match, add an event listener for its change event that will handle processing the stylesheet if it were to become applicable according the media query.

No files, tests, or entry points are named. Start by locating the polyfill code that processes stylesheet links, then trace its handling of disabled and media attributes; done means inapplicable stylesheets are not processed until their state changes or their media query matches.