Compiler and tools version updates not reported

[DavidGoodenough]

dependencyUpdates current report library dependency updates, and with a little slight of hand plugin updates. It would be really useful if it could also report compiler and sbt updates.

Compiler updates used to be obvious from the standard library being out of date, but with Scala-3 this is no longer true.

It would be easiest from a user point of view if dependencyUpdates reported all three groups in one report. This would ideally be structured with a group heading (library, plugin, tools) and then under each heading the relevant updates.