Apply all backwards-compatible dependency upgrades

We're depending on quite a few outdated dependencies. This commit updates all dependencies where the upgrade should be non-breaking (so only minor versions). I've read through the changelogs and could indeed not find any backwards-incompatible changes that would affect us.

I had to do 2 changes that were enforced by the newer TypeScript version enabling additional checks. The changes should not change behavior though. I superficially checked that bringing up the frontend and navigating the site still works.

@types/pdfjs-dist was removed, since pdfjs-dist now provides its own type definitions (https://www.npmjs.com/package/@types/pdfjs-dist).