Volumetric Lightmaps do not work with Landscape texture mapping

It appears that the Lightmass Volumetric Lightmap does not work with Landscape textures. When it samples the Landscape with some textured material, the resulting lighting build data does not match the actual texturing of the landscape at all.

This issue was reported and tested in 4.21.2 (CL-4753647). This was reproduced in 4.20.3 (CL-4369336), 4.22 (CL-4958363), and Main 4.23 (CL-4982248)

1. Download and open the attached project
2. Open up the "Landscape_Repro" map, build the lighting, and enable Volumetric Lightmap (Show>Visualize>Volumetric Lightmap)
3. Observe that the Lightmass Volumetric Lightmap does not have colors matching the colors of nearby Landscape texture
4. Open the "MeshPlane_Repro" map, build the lighting, and enable Volumetric Lightmap
5. Observe that the Lightmass Volumetric Lightmap has the colors matching the colors of nearby static mesh plane

Results: Lightmass Volumetric Lightmap indirect light from the landscape is wrong, not matching the texture on the landscape surface.

Expected: Lightmass Volumetric Lightmap indirect light from the landscape is correct, having the same result as indirect light from the static mesh plane of same position, size and material.