Adding mermaid.js support via markdown-it.

[dessalines]

• Fixes Add support for Mermaid.js diagrams #2754

EDIT: nm, this doesn't work currently because the library doesn't support ESM :

Error [ERR_REQUIRE_ESM]: require() of ES Module /home/xxx/git/lemmy-ui/node_modules/.pnpm/[email protected]/node_modules/mermaid/dist/mermaid.core.mjs not supported.

[Nutomic]

This is for some sort of diagram rendering? I would rather not add that because its pretty much out of scope, and then all other frontends and apps would also have to add support for this feature.

[dessalines]

Yep. Here's some more cool ones that hedgedoc for example supports in their markdown.

I think its fine if we have these markdown add-ons, as long as its understood that we won't maintain the libraries ourselves, and that any apps will have to do their own work supporting them. It could also be kind of a cool incentive / project for people to start adding these renderers to other platforms besides the web, like android / iOS.