fetchurl: refresh and add extra KDE mirrors

* fetchurl: fix and add extra KDE mirrors (#51480)

- The gwdg.de mirror has moved the relative path of its KDE tarballs
- Add new mirrors from Berkeley and MIT, which are on the list of officially supported mirrors

https://download.kde.org/extra/download-mirrors.html

* More KDE mirror touchups

- The official one is a redirect to HTTPS anyways, so go directly to HTTPS
- Add China USTC for Asian users
- Swap Finland university from FTP to HTTP

* fetchurl: keep one ftp KDE mirror