Added "[sheet" to the texture special commands.

"[sheet:WxH:X,Y" assumes the base image is a tilesheet with W*H tiles
on it and crops to the tile at position X,Y.  Basically it works
like "[verticalframe" but in 2D.

For testing, I combined the four default_chest images into one.

games/minimal/mods/default/init.lua

@@ -1130,8 +1130,9 @@ minetest.register_node("default:sign_wall", {
 
 minetest.register_node("default:chest", {
 	description = "Chest",
-	tiles ={"default_chest_top.png", "default_chest_top.png", "default_chest_side.png",
-		"default_chest_side.png", "default_chest_side.png", "default_chest_front.png"},
+	tiles ={"default_chest.png^[sheet:2x2:0,0", "default_chest.png^[sheet:2x2:0,0",
+		"default_chest.png^[sheet:2x2:1,0", "default_chest.png^[sheet:2x2:1,0",
+		"default_chest.png^[sheet:2x2:1,0", "default_chest.png^[sheet:2x2:0,1"},
 	paramtype2 = "facedir",
 	groups = {snappy=2,choppy=2,oddly_breakable_by_hand=2},
 	legacy_facedir_simple = true,
@@ -1164,8 +1165,9 @@ end
 
 minetest.register_node("default:chest_locked", {
 	description = "Locked Chest",
-	tiles ={"default_chest_top.png", "default_chest_top.png", "default_chest_side.png",
-		"default_chest_side.png", "default_chest_side.png", "default_chest_lock.png"},
+	tiles ={"default_chest.png^[sheet:2x2:0,0", "default_chest.png^[sheet:2x2:0,0",
+		"default_chest.png^[sheet:2x2:1,0", "default_chest.png^[sheet:2x2:1,0",
+		"default_chest.png^[sheet:2x2:1,0", "default_chest.png^[sheet:2x2:1,1"},
 	paramtype2 = "facedir",
 	groups = {snappy=2,choppy=2,oddly_breakable_by_hand=2},
 	legacy_facedir_simple = true,