- Switch to the modern maven-publish plugin.
- Bump the Android target SDK version to 30 to match the app.
(The minimum is still 19.)
- Bump the Java source compatibility version to 1.8.
- Bump the Android command line tools used in Docker to match the app.
- Bump the JDK used in Docker to OpenJDK 11, matching the app.
- Switch to the androidx testing libraries for emulator testing.
- Drop unused trove4j Gradle plugin.
- Lots of cleanup and refactoring.
Debian has a more stable retention period for pinned dependencies (the
version of OpenJDK 8 we were using for Ubuntu is gone already!), and
it matches what the Signal-Android repository is doing.
