fix(worldgen): give the stronghold room chest a block entity (#2543)

The chest in the stronghold square room was placed as a bare block state,
so no chest block entity was ever created for it. Opening a chest and
resolving a double chest both go through `get_block_entity`, so the chest
could neither be opened nor paired with a chest placed next to it.

Use the existing `add_chest` helper, which writes the block state and the
matching block entity with a loot table, as the nether fortress corridors
already do. Vanilla `StrongholdPieces$RoomCrossing` uses
`chests/stronghold_crossing` at the same position.

pumpkin-world/src/generation/structure/structures/stronghold/square_room.rs

@@ -24,6 +24,10 @@ use crate::{
 
 use crate::world::WorldPortalExt;
 
+/// Loot table of the chest in the room variant that has one, matching vanilla
+/// `StrongholdPieces$RoomCrossing`.
+const CROSSING_LOOT_TABLE: &str = "minecraft:chests/stronghold_crossing";
+
 pub struct SquareRoomPiece {
     piece: StrongholdPiece,
     room_type: u32,
@@ -272,8 +276,7 @@ impl StructurePieceBase for SquareRoomPiece {
                 inner.add_block(chunk, ladder, 9, 3, 3, &box_limit);
 
                 // Chest
-                // p.add_chest(chunk, &box_limit, random, 3, 4, 8, LootTables::StrongholdCrossingChest);
-                inner.add_block(chunk, Block::CHEST.default_state, 3, 4, 8, &box_limit);
+                inner.add_chest(chunk, &box_limit, random, 3, 4, 8, CROSSING_LOOT_TABLE);
             }
             _ => {}
         }