JsonParser: handle class and primitive unions

[tefra]

Closes #369

[codecov]

Codecov Report

Merging #370 (5faee9a) into master (c31e7c4) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #370   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           70        70           
  Lines         5671      5680    +9     
  Branches       997      1000    +3     
=========================================
+ Hits          5671      5680    +9     

Impacted Files	Coverage Δ
xsdata/formats/dataclass/parsers/json.py	100.00% <100.00%> (ø)

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication