FDN-3186 Update scala3 union support for primitive types

[jackl]

Adds a de-serializer for the wrapper type in a union when it is a primitive type. Without it, parsing of the response_code type fails with errors, for example:

 apibuilder upload flow api-internal /tmp/flow-api-internal.json --version 0.24.10
Uploading /tmp/flow-api-internal.json to http://localhost:9001/flow/api-internal/0.24.10 ... 
ERROR 409: Unprocessable Entity
 - Response code must be an integer or the keyword 'default' and not[{"integer":{"value":200}}]
 - Response code must be an integer or the keyword 'default' and not[{"integer":{"value":401}}]
 - Response code must be an integer or the keyword 'default' and not[{"integer":{"value":404}}]
 - Response code must be an integer or the keyword 'default' and not[{"integer":{"value":422}}]
 - Response code must be an integer or the keyword 'default' and not[{"integer":{"value":201}}]

[mbryzek]

lgtm