Porting away from PlasmaCore.Units, PlasmaCore.Theme, and PlasmaCore.ColorScope

We don't have to use these because they have Kirigami equivalents now, and have been removed in https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/854.

Here are the MRs porting away from them:

• https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/819
• plasma-desktop!1574 (merged)
• plasma-desktop!1604 (merged)
• !3045 (merged)
• !3210 (merged)
• kdeplasma-addons!418 (merged)
• kdeplasma-addons!428 (merged)
• plasma-sdk!84 (merged)
• plasma-sdk!91 (merged)
• plasma-nm!264 (merged)
• plasma-pa!186 (merged)
• plasma-pa!196 (merged)
• bluedevil!132 (merged)
• plasma-vault!30 (merged)
• kscreen!219 (merged)
• milou!63 (merged)
• milou!68 (merged)
• plasma-welcome!98 (merged)
• polkit-kde-agent-1!28 (merged)
• powerdevil!212 (merged)