Also added a unit test to verify that decryption without a license fails
with the correct error code. Also changed comment types for policy
integration tests and core integration tests to be picked up by Doxygen.
Bug: 320785945
Merged from https://widevine-internal-review.googlesource.com/194910
Change-Id: Ibdb70683003bb430dde9b4a1bd9fc9839bace342
(cherry picked from commit d05d3738b4)