Allow inflation_layer inheritance

[BriceRenaudeau]

The obstacles_critics of MPPI and SMAC_planner are tightly related to the nav2_costmap_2d::InflationLayer.

https://github.com/ros-planning/navigation2/blob/2f1f9e4a225f912c4c1ae9821fb7eb31ac192c16/nav2_mppi_controller/src/critics/obstacles_critic.cpp#L52-L55

To use a custom version of the inflation layer with the MPPI/SMAC, the custom layer needs to inherit from the inflation layer.
But the inflation_layer isn't adapted to inheritance, there are private members and methods.

Required Info:

• Operating System:
  • Ubuntu 22.04
• ROS2 Version:
  • Iron
• Version or commit hash:
  • main
• DDS implementation:
  • cycloneDDS

Expected behavior

When using a child class of inflation_layer, all the methods should work.

Actual behavior

When using a child class of inflation_layer, the attributes are not shared, so some methods, like getCostScalingFactor(), don't return the real value.

Implementation considerations

We fixed this by removing the private: keyword in the inflation_layer header file.

https://github.com/ros-planning/navigation2/blob/2f1f9e4a225f912c4c1ae9821fb7eb31ac192c16/nav2_costmap_2d/include/nav2_costmap_2d/inflation_layer.hpp#L185-L191C9

[SteveMacenski]

Perhaps just make private protected so derived classes can use them? Seems very reasonable to me!

[SteveMacenski]

#3722