[Bug]: Avro schema support doesn't support UNION types (OneOf) for SpecificRecords

### What happened?

`AvroRecordSchema.fromRowFunction` fails if a `SpecificRecord` contains a field with a UNION type. Reason is that the necessary type information (`FieldValueTypeInformation.getOneOfTypes`) required for `FromRowUsingCreator` isn't populated.

### Issue Priority

Priority: 2 (default / most bugs should be filed as P2)

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