Group associated compilations into modules with a single module name

As associated compilations will see internals of each other, they now
need to share the module name for the compiler to be able to correctly
generate calls to the internals.

Move `moduleName` to `KotlinCompilation`.

Group associate compilations into modules in a DSU-like way, use a
single module name for all of the compilations grouped into a module.

libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinCompilation.kt

@@ -75,6 +75,8 @@ interface KotlinCompilation<out T : KotlinCommonOptions> : Named, HasAttributes,
 
     override val relatedConfigurationNames: List<String>
         get() = super.relatedConfigurationNames + compileDependencyConfigurationName
+
+    val moduleName: String
 }
 
 interface KotlinCompilationToRunnableFiles<T : KotlinCommonOptions> : KotlinCompilation<T> {