NavMap InflationFilter: inflate from 3D distances to the real border

[fmrico]

Fixes #113

Depends on EasyNavigation/NavMap#33 (NavMap::distance_field). CI will fail until that PR is merged into NavMap rolling.

The NavMap InflationFilter now takes its distances from NavMap::distance_field:

• 3D distances along the surface, to the obstacle cells and, with inflate_borders (new, default true), to the open edges of the mesh as real segments;
• border cells are no longer lethal as a whole: they get the cost of their real distance to the edge;
• ramps get their true (3D) distances;
• an obstacle on one floor does not inflate the floor above;
• the costmap_2d cost formula is unchanged, and unknown cells keep their value and carry the distance as before.

Validation

Parking garage playground (multi-level NavMap at 0.4 m, ramps 2.9 m wide between side walls, 0.7 m inscribed radius):

• before: the planner found no path to the upper floors, because the ramps came out blocked;
• after: the Summit reaches floor 1 (62 s) and floor 2 (129 s).

Battery of the other NavMap playgrounds: unchanged.

Playground	Before	After
Summit excavation	FINISHED, 0.58 m	FINISHED, 0.60 m
TIAGo house	FINISHED, 0.18 m	FINISHED, 0.17 m
Summit warehouse	FINISHED	FINISHED

The warehouse time varies with an RPP issue at the goal (#115), not with this change.

Tests

5 new tests:

• border cells are not lethal and cost by their real distance;
• a narrow corridor keeps its true width;
• inflate_borders: false;
• slope distance along the surface;
• an obstacle on one floor does not inflate the floor above.

The existing inflation tests pass unchanged.