Add type checking to JSON serializer

[pnoltes]

Add JSON type checking to the JSON (de-)serializer. Although remote services is based on trusted entities, type checking can help in finding bugs especially if messages interfaces are updated.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.63%. Comparing base (270c784) to head (26adf35).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #850      +/-   ##
==========================================
+ Coverage   91.54%   91.63%   +0.09%     
==========================================
  Files         235      235              
  Lines       28787    28826      +39     
==========================================
+ Hits        26353    26415      +62     
+ Misses       2434     2411      -23     

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[PengZheng]

LGTM