Draft: Fix system tray popup position

Hello. There was an issue with the system tray where clicking on items only showed the popup for 1 frame. I changed the positioning to be based on the currentHighlight, but that might be a wrong fix, so I marked this as a draft. (I don't have any experience with plasma stuff but I took a shot at fixing it anyway)

This problem was experienced in wayland, plasma 6.4.5, kde frameworks 6.18.

After this fix, it works as expected.