Material overrides not respected when generating HLODs.

When generating HLODs, it is possible for the generator to ignore material override settings.
The generator will not respect the constants, and does not change them in the Material with a default setup.

1. Download the attached test project and open.
2. Observe the material "/Game/M_SphereMat" has its roughness set to 1.
3. Observe in /Game/TestMap_HLOD1_Approximate", the Material settings are set to use constant 1 for roughness.
4. Load the region of the world containing the Actor "Sphere". It's on the right side of the World Partition minimap.
5. Observe that the sphere does have high roughness.
6. Unload the sphere.
7. Build HLODs.
8. Observe the HLOD of the sphere. Notice that it has low roughness.
9. Observe the Material Instance on the HLOD. It is not overriding roughness.