proposal: server managed vanilla item id

[smartcmd]

Overview

Currently, for vanilla item types, Allay assigns the same runtime ids as the vanilla. However, since item id is decided server-side, we can just use an id counter to assign the runtime id. This change will remove the runtimeId field in ItemId enum to prevent users from using these numerical ids, as these numerical ids are not expected to be used by users (they may change between different protocol version).

Although in most of the cases, the protocol layer have stop using numerical ids, the effect of this change is unknown. Most of the 3rd bedrock server implementation still using the same runtime id as the vanilla. Before further work, it is necessary to investigate the unintended impacts this change may result from.