Add some more test coverage to verify the IDE plugins are consistent in how they behave in composite builds. This just covers a couple of simple scenarios. Change the `eclipse` task of the root project so that it generates the Eclipse projects for all builds, and so produces usable project files when there are included builds.
Add some test coverage to verify that each of the IDE plugins can be applied to `buildSrc`. Start growing some cross-cutting test coverage for the IDE plugins, so the plugins can become less different to each other.