* Upgrade Kotlin to match the version used by Briar, to fix
  Briar's mailbox integration tests
* Upgrade Hilt for compatibility with Kotlin 1.9
* Upgrade Android Gradle Plugin so that R8 can understand metadata
  produced by Kotlin 1.9
* Upgrade Java version (and thus JVM requirement for building) to
  match the version used by Kotlin

I also upgraded Jackson while getting JacksonProguardTest to pass,
which may or may not have been necessary (upgrading AGP may have
been what did the trick).