message: Expose isTwoSided flag on ExportGraphicsMesh
  Useful for clients to know whether backface culling can be safely enabled.
diff: @@ -76,6 +76,8 @@ export interface ExportGraphicsMesh {
  normals: Float32Array;
  /** Parameters (uvs) for this mesh, laid out in the pattern XYXY */
  params: Float32Array;
  + /** If true, clients should assume both sides of the mesh are visible and not cull backfaces. */
  + isTwoSided: boolean;
  }
  /** Info provided to ExportGraphicsFunction about graphics.
  