[css-fonts-4] Add CBDT, resolves w3c#4919

Author: svgeesus

css-fonts-4/Overview.bs

@@ -1877,7 +1877,7 @@ The <dfn id="at-font-face-rule">''@font-face''</dfn> rule</h3>
 
     <pre class="prod"><dfn id="font-technology-values">&lt;font-technology&gt;</dfn> = [features | variations | color(<<color-font-technology>>) | palettes]</pre>
 
-    <pre class="prod"><dfn id="color-font-technology-values">&lt;color-font-technology&gt;</dfn> = [COLR | SVG | sbix]</pre>
+    <pre class="prod"><dfn id="color-font-technology-values">&lt;color-font-technology&gt;</dfn> = [COLR | SVG | sbix | CBDT ]</pre>
 
     If parsing a particular item in the split value results in a parse error,
     that item is thrown out.