A combination of a few changes:
- Don't apply hardness again, the "cube tip" calculation already factors it in.
- Avoid multiplication by brush radius, just use the 0-1 distances from the
cube tip calculation directly.
- Add filtering by brush radius to fix the second part of #128004.
- Change brush radius filtering to be consistent with previous code using
less than or equal instead of less than.
Note that the current radius filtering in BKE_brush_calc_curve_factors is
unnecessary since we already filter by the radius in a separate step.
6d9641daee