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

compiler/testData/codegen/light-analysis/defaultArguments/function/innerExtentionFunction.txt

@@ -1,3 +1,4 @@
+@kotlin.Metadata
 public final class A {
     public method <init>(): void
     public synthetic static method foo$default(p0: A, p1: int, p2: int, p3: int, p4: java.lang.Object): int
@@ -5,6 +6,7 @@ public final class A {
     public final @org.jetbrains.annotations.NotNull method test(): java.lang.String
 }
 
+@kotlin.Metadata
 public final class InnerExtentionFunctionKt {
     public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
 }