Core tileset sound handling

Currently, `SolidTiles` special-cases the tileset ID `k` (`core` tileset in vanilla) to bypass `SurfaceIndex.TileToIndex` entirely and use 37, 38, or 3 as sound index depending on core mode. Tile entities do not use this special handling, which means if core mode is active, core tile entities will sound different from solid tiles. Additionally, this means any custom tileset using the ID `k` will always use core tileset sounds regardless of `sound` attribute. At least the tile entities handling should be fixed. Potentially, the custom tileset handling could also be addressed, maybe even providing a way for custom tilesets to vary sound based on core mode.