feat: scene ghosting, as the client streams a zone's scenes

The client keeps the scene under the player loaded, the scenes the zone
file's transitions connect to it, and the global scene
(Zone::StreamScenesAroundPosition 0x0108a3f0, TerrainManager::GetSceneAtPos
0x01069010, the connected scenes at 0x01066500; transitions naming a
missing scene dropped as Zone::FixupInvalidTransitions 0x010842e0 does).

- ZoneScenes (dCommon): the terrain's scene map lookup and the scene graph,
  shared by the world server and the dashboard.
- Objects remember the scene they were placed in (spawners pass theirs on).
- ghosting_scenes=1 (world config, off by default): players get the objects
  of their loaded scenes instead of the ones within the ghosting distances;
  objects from no scene go by the scene under them. Zones without a scene
  map keep distance ghosting.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/dCommonTests/CMakeLists.txt

@@ -22,6 +22,7 @@ set(DCOMMONTEST_SOURCES
 	"ScheduleRulesTests.cpp"
 	"VanityEventsTests.cpp"
 	"ZoneFileTests.cpp"
+	"ZoneScenesTests.cpp"
 	"LiveOpsRulesTests.cpp"
 	"ProcessAndLimitsTests.cpp"
 	"HotPropertySlotsTests.cpp"