Misleading function names: ExportSurface(s)ForDisplay

[dmcconachie]

The following 2 functions could potentially benefit from a rename

visualization_msgs::Marker ExportSurfacesForDisplay(
    const CollisionMap& collision_map,
    const std_msgs::ColorRGBA& collision_color,
    const std_msgs::ColorRGBA& free_color,
    const std_msgs::ColorRGBA& unknown_color)

visualization_msgs::Marker ExportSurfaceForDisplay(
    const CollisionMap& collision_map,
    const std::unordered_map<
        common_robotics_utilities::voxel_grid::GridIndex, uint8_t>& surface,
    const std_msgs::ColorRGBA& surface_color)

In general the 2nd function can export any arbitrary set of points, not just a surface. These could probably benefit from some renaming or at least some comments of some sort describing what they actually do and how they are intended to be used (mostly for the 2nd function). It's not clear what the surface input should be.

(and matching changes in ExportVoxelGridSurfaceToRViz and similar functions)

[calderpg]

I have renamed these functions from Surface to IndexMap for the time being before more detailed doxygen is added.