Unit Motion - Improve handling of obstructed paths.

Units right now try going to their next long waypoint using the short-range pathfinder. This works, but it tends to leads to units clumping together when shuttling for example.

By switching to short paths earlier, and by scrapping the long waypoints when doing so, we can make movement more natural until we have unit pushing.

Some cleanup in how the short-path domain range gets handled, and increase the max-range by one tile to improve rare cases.

Differential Revision: https://code.wildfiregames.com/D2095