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

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

@@ -1,3 +1,4 @@
+@kotlin.Metadata
 public final class A {
     public final static field INSTANCE: A
     private method <init>(): void
@@ -6,6 +7,7 @@ public final class A {
     public final @org.jetbrains.annotations.NotNull method test(): java.lang.String
 }
 
+@kotlin.Metadata
 public final class ExtentionFunctionInObjectKt {
     public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
 }