homescreen/folio: Rewrite

Rewrite of the Folio homescreen such that it is predictable and deals well with different screen sizes and rotations, as well as with drag and drop. It moves the vast majority of logic to C++, trying to only have QML be only for visuals and animations.

Instead of having a large canvas in the existing folio, all elements are tied to a page with preset rows and columns (which get swapped between landscape and portrait).

This fixes issues where every time the screen is rotated or scaling is changed, the entire homescreen configuration layout gets permanently changed or bricks the shell.

This also makes folio work in Plasma 6 (it is currently broken)

For kdesrc-build upgrading from an older plasma version, be sure to run:

$ rm -rf ~/kde/usr/lib64/qml/org/kde/private/mobile/homescreen/folio