Make all immobiles have no radar drift.

[saurtron]

Work done

• Make immobile units have no radar drift

Related issues

• Conturrets are mobile units (?) Beyond-All-Reason#3617

Note I also intend to later work on the problem of nanos can't be buildings (#1597), but making ghosts also not drift or dissapear from radar for any immobile sounds more than reasonable behaviour.

Remarks

• Marking as DRAFT to validate the general approach before dedicating more work to this.
• This still needs a bitmore work to make it behave completely right:
  • change ghostedBuildings to ghostedImmobiles (and export/accept also ghostedBuildings alias for now).
  • adapt also UnitDrawerData.cpp and GroundDecalHandler.cpp (and maybe some other places) so the ghosts won't go away like with buildings.

Open problems

• Whats the best way to handle the situation where the building/immobile is actually moved for any reason, like transport
• Also whats the best way to give lua fine grained control over this, unitDef?, unit flag?
  • probably need something at unit itself, since many times override will need to be done per unit

Reference

IsImmobileUnit -> (pathType == -1U && !canfly && speed <= 0.0f)
IsBuildingUnit -> (IsImmobileUnit() && !yardmap.empty())
IsGroundUnit   -> (pathType != -1U && !canfly)

[sprunk]

This just forces immobiles to have ghosts while leaving games no control. Add a new unit def tag, bool leavesBuildingGhost, and make ghosts look for that.

That tag should default to true for buildings and false for mobiles, but I dug a bit and I'm no longer sure whether that new tag should default to true for immobiles. See 30c07c5, e573bdb, and https://springrts.com/mantis/view.php?id=6127.