DM: offer Eucledian distance between objects

Problem description

the object_distance() method offers longitudinal and lateral directions, but not Eucledian.

This is already offered in OSC1.x In RelativeDistanceType.

Should be supported in OSC2

Proposed solution

With the current 2.0 spec, this method could be implemented (e.g., using the results of object_distance() in lateral and longitudinal directions)

In 2.1+ this option could be added to the method

Reported by @najumun.hidhayathulla in Implementer's Forum