GeoModelUtilities: Add a size hint to geoGetVolumes.
Add an additional optional argument to geoGetVolumes as a hint on the number of volumes to be returned. If the caller already knows this, then this can allow avoiding some vector resizes.
Add an additional optional argument to geoGetVolumes as a hint on the number of volumes to be returned. If the caller already knows this, then this can allow avoiding some vector resizes.