astar_search implicitly requires DistanceType to be a primitive type

[Luis G. Torres <lgtorres42@…>]

The astar_search function can optionally take as an argument a value to use as distance_inf. However, if the Distance value type is anything besides the primitive numeric types, a compiler error gets thrown due to line 441, where it tries to specialize the std::numeric_limits template using the Distance value type. Hopefully, there should be a way to specify a default distance_inf value without requiring more general types to be primitive types.

[Jeremiah Willcock]

(In [84028]) Added support for distance types without numeric_limits specializations; changed test to use that functionality to ensure that it keeps working; fixes #8490