Kotlin Facet: Track configuration version

idea/idea-jps-common/src/org/jetbrains/kotlin/config/KotlinFacetSettings.kt

@@ -76,6 +76,12 @@ class KotlinCompilerInfo {
 }
 
 class KotlinFacetSettings {
+    companion object {
+        // Increment this when making serialization-incompatible changes to configuration data
+        val CURRENT_VERSION = 1
+        val DEFAULT_VERSION = 0
+    }
+
     var versionInfo = KotlinVersionInfo()
     var compilerInfo = KotlinCompilerInfo()
 }