Add libjsonpbverify.

- libjsonpbverify is a helper library that a gtest can link against
  when checking JSON files against their protobuf schema.

- Add unittests to ensure these validation functions are correct.
  (libjsonpbverify_test)

- Add tests to mitigate discrepancies of behavior between libjsoncpp
  and libprocessgroup. (libjsonpbverify_test)

- Add tests to impose additional restrictions on proto3 files when
  using them as JSON schema.

Test: libjsonpbverify_test

Bug: 123664216
Change-Id: I1e6257c9a25fd8d10fad103f3b74f7e1c6fad8a6
8 files changed