Runtime_identifier tag for custom blocks

For now many of the features that you would like to attribute to custom blocks are still hard coded. This also applies to custom entities even if in a smaller amount. But these have the ability to have the hard-coded features of vanilla mobs through the runtime_identifier tag. It would be very useful to be able to use this system also with blocks, thus being able to assume the behavior of a ladder, a trapdoor or a log.