Move JvmTarget to frontend.java, introduce TargetPlatformVersion

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

compiler/cli/cli-common/cli-common.iml

@@ -10,6 +10,6 @@
     <orderEntry type="module" module-name="util" />
     <orderEntry type="library" scope="PROVIDED" name="intellij-core" level="project" />
     <orderEntry type="library" name="jps" level="project" />
-    <orderEntry type="module" module-name="descriptor.loader.java" />
+    <orderEntry type="module" module-name="frontend.java" />
   </component>
 </module>