Draft: taskswitcher: refactor to make it work with qmlcachegen

after seeing the recent kdab article https://www.kdab.com/10-tips-to-make-your-qml-code-faster-and-more-maintainable/ (and being personally bothered by some stuff in the mobile task switcher code) I wanna refactor it to improve performance.

Still very unfinished, but made the MR because I need to focus on some other things for a few days so if someone really wants to take this they don't need to start quite from 0. (I don't guarantee anything here is functional though 😀 )