[KPM] Implement initial IdeaKotlinProjectModelBuilder

- Introduce `kotlin-gradle-plugin-idea` module that allows
to share models between the IDE and KGP

- Add `kotlin-gradle-plugin-idea` to the RuntimePublicAPITest to
ensure binary compatibility

^KT-51262

libraries/tools/kotlin-project-model/src/main/kotlin/KotlinModule.kt

@@ -7,8 +7,7 @@ package org.jetbrains.kotlin.project.model
 
 import java.io.Serializable
 
-// TODO sealed with an abstract subclass? this will make exhaustive checks work
-open class KotlinModuleIdentifier(open val moduleClassifier: String?): Serializable
+sealed class KotlinModuleIdentifier(open val moduleClassifier: String?): Serializable
 
 // TODO consider id: Any, to allow IDs with custom equality?
 data class LocalModuleIdentifier(