Add data.api.schema.NormalizedYangData

rc:yang-data extension, as delivered in YANGTOOLS-1443, requires a yang.data.api representation. Unlike all previous bits of data, this cannot be identified by a PathArgument, because the identifier is a plain String, hence we cannot reliably form a QName.

We really want something like this:

For this to happen we need to disconnect DataContainerNode from Identifiable<PathArgument> and also have to figure out what to do about NormalizationResult, as that carries a NormalizedNode as the data component, whereas we want to hold either a NormalizedYangData.