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

compiler/testData/codegen/light-analysis/defaultArguments/private/memberExtensionFunction.txt

@@ -1,3 +1,4 @@
+@kotlin.Metadata
 public final class A {
     inner class A/B
     public method <init>(): void
@@ -5,6 +6,7 @@ public final class A {
     private final method foo(p0: int, p1: int): int
 }
 
+@kotlin.Metadata
 public final class A/B {
     synthetic final field this$0: A
     inner class A/B
@@ -12,6 +14,7 @@ public final class A/B {
     public final method bar(): int
 }
 
+@kotlin.Metadata
 public final class MemberExtensionFunctionKt {
     public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
 }