refactor(core): Simplify JSON encoding of DataValue and DiagnosticInfo
refactor(core): Simplify JSON encoding of DataValue and DiagnosticInfo

jpfr/open62541,JGrothoff/open62541,jpfr/open62541,open62541/open62541,JGrothoff/open62541,jpfr/open62541,JGrothoff/open62541,JGrothoff/open62541,jpfr/open62541,open62541/open62541,open62541/open62541,open62541/open62541