Make insertBefore() update pointers to the object from other language definitions.
Use case/Example: In dabblet, code-highlight.js adds some extra tokens to CSS. But CSS also extends markup to highlight CSS in style elements/attributes and that happens *before* the extra CSS tokens were added. However, because references were not updated, CSS highlighted in markup was using the original CSS definition, without the added tokens. I’m surprised we haven’t caught this earlier, I’d expect it to affect many advanced uses of Prism.