Add NavigationRegion costs for 2D and 3D pathfinding

[smix8]

Adds NavigationRegion costs for pathfinding in 2D and 3D.

Each navigationregion has two new properties.
Fixed enter_cost value for entering this region from a different region e.g. entering from "ground" region to "water" region.
Distance based travel_cost multiplier for moving on the same navmesh.

Note that since 2D converts pixel units to full 3D world pathfinding units on the navigationmap the 2D travel_cost has a tremendous effect and the 2D enter_cost value needs to be increased dramatically compared to 3D for a similar pathfinding result.

Godot 4.0 TestProject for 2D and 3D:
NavigationRegionCostTestMap.zip

[smix8]

I ... have no idea what is causing this one linux build to fail, help!

[akien-mga]

The error is:

servers/navigation_server_2d.cpp:57:2: error: no declaration matches 'void NavigationServer2D::region_set_enter_cost(RID, real_t) const'
   57 |  NavigationServer2D::FUNC_NAME(T_0 D_0, T_1 D_1)                                      \
      |  ^~~~~~~~~~~~~~~~~~
servers/navigation_server_2d.cpp:247:6: note: in expansion of macro 'FORWARD_2_C'
  247 | void FORWARD_2_C(region_set_enter_cost, RID, p_region, real_t, p_enter_cost, rid_to_rid, real_to_real);
      |      ^~~~~~~~~~~

So you seem to have a mismatch between a prototype and a macro. Maybe argument arity, type, or constness mismatch.

[akien-mga]

Maybe clash between using float and real_t in different places. The failing CI builds uses double=64 i.e. real_t is double.

[akien-mga]

CC @AndreaCatania @Scony

[akien-mga]

Thanks!