The USD Preview Surface material import feature is now considered
stable, so this patch removes this option from the Experimental
category in the UI.
The Import USD Preview option is now enabled by default.
The Experimental box has been removed.
A new Materials box has been added to group the Import
USD Preview Surface, Set Material Blend and Material
Collision Mode options.
Reviewed by: Sybren
Differential Revision: https://developer.blender.org/D17053
e49e5f6f08