Let CSS Color handle CSS <color> value parsing

Our definition had issues such as not resolving currentcolor correctly when used as part of CSS color functions.

Fixes #9940.

source

@@ -3520,31 +3520,6 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
  parenthesis and a missing "blue" value) cannot be parsed, as closing the open construct does not
  result in a viable value.</p>
 
- <p>To <dfn id="parsed-as-a-css-color-value">parse a CSS &lt;color> value</dfn>, given a string
- <var>input</var> with an optional element <var>element</var>, run these steps:</p>
-
- <ol>
- <li><p>Let <var>color</var> be the result of <span data-x="parse something according to a CSS
- grammar">parsing</span> <var>input</var> as a CSS <span>&lt;color></span>.
- <ref>CSSCOLOR</ref></p></li>
-
- <li><p>If <var>color</var> is failure, then return failure.</p></li>
-
- <li>
- <p>If <var>color</var> is <span>'currentcolor'</span>, then:</p>
-
- <ol>
- <li><p>If <var>element</var> is not given, then set <var>color</var> to <span>opaque
- black</span>.</p></li>
-
- <li><p>Otherwise, set <var>color</var> to the computed value of the <span>'color'</span>
- property of <var>element</var>.</p></li>
- </ol>
- </li>
-
- <li><p>Return <var>color</var>.</p></li>
- </ol>
-
  <p>The following terms and features are defined in <cite>Cascading Style Sheets</cite>
  (<cite>CSS</cite>): <ref>CSS</ref></p>
 
@@ -3649,6 +3624,7 @@ a.setAttribute('href', 'https://example.com/'); // change the content attribute
  <li><dfn data-x-href="https://drafts.csswg.org/css-color/#valdef-color-srgb">'srgb'</dfn> color space</li>
  <li><dfn data-x-href="https://drafts.csswg.org/css-color/#valdef-color-display-p3">'display-p3'</dfn> color space</li>
  <li><dfn data-x-href="https://drafts.csswg.org/css-color/#valdef-color-profile-rendering-intent-relative-colorimetric">'relative-colorimetric'</dfn> rendering intent</li>
+ <li><dfn id="parsed-as-a-css-color-value" data-x-href="https://drafts.csswg.org/css-color/#parse-a-css-color-value">parse a CSS &lt;color> value</dfn></li>
  </ul>
 
  <p>The following terms are defined in <cite>CSS Images</cite>: <ref>CSSIMAGES</ref></p>