Make TNT respect on_blast, implement on_blast for some nodes

Implemented nodes:
- Steel Door: Ignores explosion
- Locked Chest: Ignores explosion
- Fire: Ignores explosion
- TNT: Starts burning
- Burning TNT: Explodes immediately
- Gunpowder: Starts burning
- Burning Gunpowder: Ignores explosion

mods/default/nodes.lua

@@ -1341,6 +1341,7 @@ minetest.register_node("default:chest_locked", {
 			)
 		end
 	end,
+	on_blast = function() end,
 })