Implement BindingCodecContext.getSubtreeCodec(Absolute)

BindingCodecTree has this neat method, but unfortunately it is not implemented. Implement it for the case of finding RpcInput and RpcOutput for a particular RPC and use it to cache codecs for both input and output.

Since we are dealing with type safety, we probably want to also expose specialized BindingDataObjectCodecTreeNode for both RpcInput and RpcOutput, so that we can type check returns.

Doing this should enable us to deprecate BindingNormalizedNodeSerializer.fromNormalizedNodeRpcData(), as that ends up being unused. If that is the case, also investigate toNormalizedNodeRpcData() callers to see if we can also migrate those – although that may end up being problematic.