Merged requested to merge work/zzag/screencast-cursor into master
XCURSOR_SIZE * scale factor is not the way to compute the current cursor size. For example, with breeze cursor theme at an output with a scale of 2 and cursor size 24, cursor images will have the effective size of (64, 64).
Also, the cursor can change when passing over user interface elements.
In order to accommodate for all of that, this change makes kwin reserve enough of space for a cursor of size 256x256. "256" is a magical number that comes from DRM. With many drivers, the maximum cursor size is 256.