Updates the normals and UV's of NewTriangles. UV's are taken from VidUVMaps, which is an array of maps (1:1 with UV layers) that map vid's of vertices on the boundary to their UV elements and values. If an entry for NewVertex is not provided, it is set to be the average of the boundary UV's. For other UV's, an entry must exist, though the UV element ID can be InvalidID if an element does not exist for that UV value. The function will update the element ID in the map to point to the new element once it inserts it.