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

compiler/testData/codegen/light-analysis/objects/objectExtendsInnerAndReferencesOuterMember.txt

@@ -1,3 +1,4 @@
+@kotlin.Metadata
 public final class A {
     inner class A/Inner
     public method <init>(): void
@@ -5,12 +6,14 @@ public final class A {
     public final @org.jetbrains.annotations.NotNull method getX(): java.lang.Object
 }
 
+@kotlin.Metadata
 public class A/Inner {
     synthetic final field this$0: A
     inner class A/Inner
     public method <init>(p0: A): void
 }
 
+@kotlin.Metadata
 public final class ObjectExtendsInnerAndReferencesOuterMemberKt {
     public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
 }