Add union example for a test with versioning

Adding a new field to a versioned union is considered as a compatible
change, but passing a union with a value of a new field can raise an
exception when the receiving side doesn't understand the new field.

Bug: 170676897
Test: aidl_integration_test
Change-Id: I8faeeb22c60c28a61d5006267371455d728359fc
15 files changed