Support CSS attributes

[adamghill]

One approach (for right now) is to never remove CSS selectors with a bracket until this works better.

More details: https://developer.mozilla.org/en-US/docs/Web/CSS/Attribute_selectors.

Example:

[aria-label][role~="tooltip"] {
    position: relative;
}

a[title] {
  color: purple;
}

Not sure if it's reasonable to store all available attributes, it might require some thought about how to store this data for the site. Especially if we want the granularity to match things like div[lang].

[adamghill]

c7d1904 added the first portion of this.