plugins/shakecursor: Port to CursorItem

Vlad Zahorodniirequested to merge
work/zzag/scene-item-transform into master

The main motivation: make the shake cursor effect stop using OpenGL and let it re-use CursorItem. Changing the size of the CursorItem won't work because SurfaceItemWayland picks its own size. Changing the scale is the next available option.

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