temp/plasma: upgrade to 5.20.1

KDE Plasma 5.19.90 is a beta release of Plasma 5.20. Fork it from Alpine so we can use it with the latest plasma-phone-components which I personally think looks very sexy now 😄

Also included a new keyboard based on Maliit. This does however mean the virtual keyboard style that was used with Qt5VirtualKeyboard for the on-device installer isn't available anymore. @bshah said he would split it out to a separate repo so when that happens I'll update this MR to include it as a new package.

Note that we can drop the Plasma forked packages again when Plasma 5.20 hits the Alpine repositories.