Use the World viewport color when rendering pose library previews.
The World's viewport color is chosen instead of the World shading nodes,
as the latter would require rendering with `OB_RENDER` (instead of
`OB_SOLID`), which would take considerably longer.
Manifest Task: T93467
Reviewed By: sybren
Differential Revision: https://developer.blender.org/D13470
6a9775ec6f