Don't include raiding units in Units::isActive; make getPosition return invalid coords

[Bumber64]

Raiding units are unflagged as inactive shortly after they leave the map, as they are removed from units.active. Scan this vector to rule out raiding units. The move_state and can_swap flags are also unset, which can be used to optimize the check.

Units::getPosition now returns invalid coords for inactive units. This impacts Units::isUnitInBox, and Units::getUnitsInBox.

It also impacts Items::getPosition, but an item in items.other.IN_PLAY has its holder is guaranteed to be active (artifact theft bugs notwithstanding).

Only iterate active units in spectate instead of all. (Mainly for efficiency. Units::isActive change would've caught any potential issue with raiding units.)

[myk002]

Units::isActive is used in many many places. I'm worried that adding an O(N) search for every call will be a performance killer. I'm also concerned that changing the behavior of this function will break existing callers, both Lua and C++. I'd like to see some research done on those two points before merging this PR.

[Bumber64]

I did a check on my fort, and all of my units in units.active had at least one of inactive, move_state, or can_swap set. There was an inactive unit without the other two flags set that had its pos directly above my well. It's possible the combination could represent a ghost or climbing unit? Probably not going to be a performance consideration given how infrequently those occur. Then there's the actual raiding units, which you won't hit while iterating units.active, and for which the check is mandatory when iterating units.all.

I went through all the uses of isActive, getPosition, getUnitsInBox, and isUnitInBox I could find, as well as the inactive flag. There's no change in behavior to anything iterating the units.active vector (or indirectly through forCitizens/getCitizens). isDead is used instead of isActive for the case of actual dead units. Anything iterating units.all wasn't properly considering raiding units, which was just RemoteTools.cpp/spectate.

I don't fully understand plugins/preserve-rooms.cpp but it didn't look like the changes break anything. You'd know better than me.