Fix xdg-mime for KDE 5 and 6

Updated Version of !47 (closed) since @panta82 seems to not be around anymore.

Similar to !15 (closed) (which only lacked support for kde6 and rebuilt the cache for every requested association change).

Inspired by https://git.adelielinux.org/adelie/packages/-/blob/current/user/xdg-utils/xdg-mime-plasma.patch

• Before merging please verify that kbuildsycoca without a version suffix is the correct command for kde 6 (@nicolasfella or @ngraham) (it wasn't, fixed)

Closes: #12 (closed)