Codechange: Add base() method to StrongType to allow access to the base type without casting. (#11445)

This removes the ability to explicitly cast to the base type, but the requirement
to use .base() means the conversion is still explicit.

src/story.cpp

@@ -99,7 +99,7 @@ static void UpdateElement(StoryPageElement &pe, TileIndex tile, uint32_t referen
 			break;
 		case SPET_LOCATION:
 			pe.text = text;
-			pe.referenced_id = static_cast<uint32_t>(tile);
+			pe.referenced_id = tile.base();
 			break;
 		case SPET_GOAL:
 			pe.referenced_id = (GoalID)reference;