Test and cleanup the disabled <link> node logic

[MatthewHerbst]

Follow up to #537

@luckrnx09 Let me know what you think!

[luckrnx09]

@MatthewHerbst Thank you for your careful consideration. I need to spend some time to study whether it can be filtered through the selector. I think I will reply to you tomorrow

[luckrnx09]

hi @MatthewHerbst , sorry for reply you so late.
Almost looks good for me, but two ideas about this PR:

1. Prefer add a rel="stylesheet" for each link tags you added in this PR, because we are importing the css files from outside.
2. We can use a selector link["stylesheet"]:not([disabled]) to filter links which has the disabled attribute, because the css will not be applied if the link has attribute disabled="false".
   See: https://codesandbox.io/s/zealous-http-0g0p4c?file=/index.html

Correct me If I am wrong

[MatthewHerbst]

I haven't been able to get the selector to work for some reason. We can revisit it in the future if we figure it out. For now I think this is good to go, and I made some improvements to the examples (tests 😉 ) as well