Update markdown-it JS package

[ssddanbrown]

Have been holding this back since it inflates bundle size by 10%, so need to see if we can properly address.
Don't think ESBuild is properly tree shaking "entities" sub package which inflates size.

I think we should be able to remove the punycode package from our own package.json, since I think this is now a specified dependency of markdown-it.

[ssddanbrown]

Decided to split out MD code instead since, when coming back to this, that's the obvious route with md code using up half of the main app bundle size. Related PR: #4930
10% as separate bundle is not really significant.