Find a way to dynamically load heavy dependencies

[acelaya]

This library uses katex, which is a big dependency that gets bundled even if you end up not using any of the code branches that use it.

Rollup supports splitting individual code bundle chunks for code that's imported dynamically via import(...), so we could do that with heavy dependencies.

This requires checking how consuming libraries can then also load those chunks on demand, since they will need to be served independently of the main bundle.

[robertknight]

Related to this, we could potentially lazily load Showdown and DOMPurify. These are only needed when annotations contain rich text in the form of HTML or markdown. For DOMPurify, we need to make sure that we do use it whenever the annotation content is rendered via dangerouslySetInnerHTML. If there is a "lite path" for text-only annotations, those should render the body as a text child.