Besides bumping the version, we can now integrate this plugin the same way we do the others. The version is now declared in the settings.gradle.kts.
The change is a bit noisy, due to needing to move our repository restrictions around.
Updating the Compose compiler must happen in lockstep with the Kotlin version, because they are tightly coupled
Kotlin 1.6 also fixes some annoying issues with Java 17, which will make first-time setup less error prone for new contributors
This only locks dependencies for Gradle plugins, but not for all of the runtime dependencies that we might have. That will be accomplished in a followup change.