Separate Normalized and Opaque metadata

Opaque metadata needs slightly different translation than NormalizedMetadata, due to two reasons:

• the exact QNameModule binding is not necessarily available in the SchemaContext which is parsing opaque anydata – XML has URI reference and JSON has module name, thus complicating addressing
• values for NormalizedMetadata are required to be native, whereas opaque metadata holds either Strings or Numbers

Refactor current definitions to account for this difference.