Move vault tiles to a separate file

lib/gen/vault_tile.dart

@@ -0,0 +1,35 @@
+part of 'generator.dart';
+
+VaultTile mergeVaultTile(VaultTile bottom, VaultTile top) {
+  if (bottom == VaultTile.wall && top == VaultTile.archpronewall) {
+    return VaultTile.wall;
+  }
+  if (bottom == VaultTile.wall && top == VaultTile.archwall) {
+    return VaultTile.wall;
+  }
+  if (bottom == VaultTile.archwall && top == VaultTile.archpronewall) {
+    return VaultTile.archwall;
+  }
+  return top;
+}
+
+LevelTile flattenVaultTile(VaultTile vt) {
+  switch (vt) {
+    case VaultTile.meta0:
+    case VaultTile.defaultwall:
+    case VaultTile.archpronewall:
+    case VaultTile.archwall:
+    case VaultTile.wall:
+      return LevelTile.wall;
+
+    case VaultTile.exit:
+      return LevelTile.exit;
+    case VaultTile.door:
+      return LevelTile.closedDoor;
+
+    case VaultTile.doorpronefloor:
+    case VaultTile.bspfloor:
+    case VaultTile.floor:
+      return LevelTile.floor;
+  }
+}