Add code to convert a CarDiagnosticEvent into Diagnostic Json

Test: runtest -x packages/services/Car/tests/carservice_test/src/com/android/car/test/CarDiagnosticManagerTest.java
      runtest -x packages/services/Car/tests/obd2_test/src/com/android/car/obd2/test/Obd2LiveFrameGeneratorTest.java
Change-Id: I3e20ed08566161763933aa6c35b1f7aa7c2feca2
7 files changed