feat: Support {CD} (#2396)

* Support {CD}

* Edit screenshotter test to fit on one page

* Update screenshots

* Remove bogus Safari screenshot

* Edit documentation to avoid tag conflicts and explain delimiters

* Add type annotations

* Add bogus safari screenshot

* Update with real Safari screenshot

* Set label vertical alignment

* Revise call to parseExpression() per PR 2085 changes to macro parsing

* Update Firefox screenshot

* Pick up review comments

* Add unit tests and snapshot.

* Tighten up label collection.

* Better loop index

* remove extra space

* Picked up comments. Added a parse check. Added a test.

Co-authored-by: ylemkimon <y@ylem.kim>
Co-authored-by: Kevin Barabash <kevinb@khanacademy.org>
Co-authored-by: Kevin Barabash <kevinb7@gmail.com>

contrib/render-a11y-string/render-a11y-string.js

@@ -647,6 +647,14 @@ const handleObject = (
             throw new Error("KaTeX-a11y: xArrow not implemented yet");
         }
 
+        case "cdlabel": {
+            throw new Error("KaTeX-a11y: cdlabel not implemented yet");
+        }
+
+        case "cdlabelparent": {
+            throw new Error("KaTeX-a11y: cdlabelparent not implemented yet");
+        }
+
         case "mclass": {
             // \neq and \ne are macros so we let "htmlmathml" render the mathmal
             // side of things and extract the text from that.