Port SymbologyImpl Esri processors to the ArcGIS 300 QFuture async API

TaskWatcher (searchSymbols/fetchSymbol/createSwatch + completion signals) -> QFuture (searchSymbolsAsync/fetchSymbolAsync/createSwatchAsync + QFutureWatcher finished/result getter); flat arcgis/ includes; arcgisversion.h shim (external SDK). advancedSymbology now builds+links vs 300 (0 errors); SymbologyXML CTest 6/6, 0 assertion failures. Migration-only vs legacy; one documented forced delta: 300 has no spec-only DictionarySymbolStyle. Summary: MIGRATION_SUMMARY_ARCGIS300_SYMBOLOGY.md.

qt6-after/qt6-migrated-legatus/Lts/Viewer/SituationMap/Map/situation_map_utils.h

@@ -13,8 +13,8 @@
 
 
 // arcgis
-#include <arcgis/SceneViewTypes.h> // SurfacePlacement
-#include <arcgis/Error.h>
+#include <SceneViewTypes.h> // SurfacePlacement
+#include <Error.h>
 
 
 // Qt