* Skeleton classes for SafetyNet and EventSurveys.

* Fix LINTs, test compile error.

* Remove lint breaking TODOs.

* Add SafetyNet requirement validation call to the attestation interface.

* Don't return salt/nonce, just offer the caller directly the PPACAndroid protobuf class.

* Add documentation, fix test build error.

* Add documentation, fix test build error.

* Add environment variables for data donation server and SafetyNet API key.

* Remove unused function.

* Fix EnvironmentSetupTest.kt