Previously JvmTarget was declared in module 'util' which is accessible
for example from 'frontend', which is not very good.
Also add a superinterface named TargetPlatformVersion which is going to
be used in platform-independent injectors in 'frontend' in the following
commits. Use it in one place (LanguageVersionSettingsProviderImpl.kt)
instead of DescriptionAware because TargetPlatformVersion sounds like a
better abstraction than DescriptionAware here
This would allow building the project with Kotlin JPS plugin on TeamCity where older library takes precendence due to appearing earlier in JPS classpath
Alexander Udalov