Upgrade Gradle, Kotlin, ProtobufJS

[ogolberg]

• Upgrade Kotlin to 1.9.20. This emits new multiplatform warnings which need to be silenced.
• Upgrade Gradle to 8.5. This requires an upgrade to the Animal Sniffer plugin. The default tool version is 1.23, so removing explicitly defined tool version. Upgrading Gummy Bears as well, while at it.
• Regenerate yarn.lock file. I was getting an error running integration tests with kotlin=1.8.22 both locally and in github actions.
• Fix a classpath collision in tests.
• Set Kotlin language level to 1.8
• Implement conversion from Kotlin Long to ProtobufJS Long (long.js) without using internal mangled properties