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

compiler/testData/codegen/light-analysis/classes/privateOuterFunctions.txt

@@ -1,3 +1,4 @@
+@kotlin.Metadata
 public final class C {
     inner class C/Inner
     public method <init>(): void
@@ -6,6 +7,7 @@ public final class C {
     public final @org.jetbrains.annotations.NotNull method foo(): java.lang.String
 }
 
+@kotlin.Metadata
 private final class C/Inner {
     synthetic final field this$0: C
     inner class C/Inner
@@ -13,10 +15,12 @@ private final class C/Inner {
     public final method innerFun(): void
 }
 
+@kotlin.Metadata
 public final class PrivateOuterFunctionsKt {
     public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
 }
 
+@kotlin.Metadata
 public interface Runnable {
     public abstract method run(): void
 }