cursor: generate sizes corresponding to more global scales

I.e. 24px x (50% 75% 100% 125% 150% 175% 200% 225% 250% 275% 300%).

This should make Breeze cursors properly sized on Wayland (at least when
using those scale factors) in GTK3 and Electron apps, and any other apps
written in toolkits that don't implement the cursor-shape-v1 protocol.

CCBUG: 448555
CCBUG: 451158