Kapt3: Write stub class files with metadata (needed for incremental compilation)

compiler/testData/codegen/light-analysis/multifileClasses/optimized/callableRefToPrivateVal.txt

@@ -1,12 +1,18 @@
+@kotlin.Metadata
 public final class BoxKt {
     public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
 }
 
+@kotlin.Metadata
+public final class a/MultifileClass
+
+@kotlin.Metadata
 synthetic final class a/MultifileClass__Part1Kt {
     private final static field ok: java.lang.String
     private final static method getOk$MultifileClass__Part1Kt(): java.lang.String
 }
 
+@kotlin.Metadata
 public final class a/OK {
     public final static field INSTANCE: a.OK
     private final static @org.jetbrains.annotations.NotNull field okRef: kotlin.reflect.KProperty0