#3827 deals with stalling when editing in the richtext editor's mathjax overlay editor. But when the plaintext editor is changed, all the mathjax custom element components are recreated* and thus rerendered on each change.

This can be much slower since now all the mathjax expressions in the field are re-rendered even if none of them were changed

The fix proposed here is to add and use lru-cache (an existing indirect dep) to cache the rendered svg. A max cache size of 10 is chosen to limit memory use, and should account for most normal usecases with <10 mathjax exprs per field

*this seems to have been noted already in #1502 (comment). it's also why the debouncing within the component has no effect here