Cache animated tile speed, use btree map for animated tiles

src/animated_tile.h

@@ -0,0 +1,23 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file animated_tile.h %Tile animation! */
+
+#ifndef ANIMATED_TILE_H
+#define ANIMATED_TILE_H
+
+#include "tile_type.h"
+#include "3rdparty/cpp-btree/btree_map.h"
+
+struct AnimatedTileInfo {
+	uint8 speed = 0;
+	bool pending_deletion = false;
+};
+
+extern btree::btree_map<TileIndex, AnimatedTileInfo> _animated_tiles;
+
+#endif /* ANIMATED_TILE_H */