* Update to Gradle 6.7 and use new toolchains feature for testing on Java versions.
* Update docs
* Add back sum
* Use GitHub test JDK for toolchain.
* Use maxJavaVersionForTests for default test version when set.
* Fix RMI
* Fix configs
* Go back to rule
* Extract variable for default Java version.
If caught with a format violation, executing `./gradlew googleJavaFormat` should fix it.
There are currently some warnings, but they’re not causing failures, so we can clean that up as we go.