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

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

@@ -1,3 +1,4 @@
+@kotlin.Metadata
 public final class Outer {
     private final @org.jetbrains.annotations.NotNull field x: Outer.Inner
     inner class Outer/Inner
@@ -5,6 +6,7 @@ public final class Outer {
     public final @org.jetbrains.annotations.NotNull method getX(): Outer.Inner
 }
 
+@kotlin.Metadata
 public final class Outer/Inner {
     synthetic final field this$0: Outer
     inner class Outer/Inner
@@ -12,6 +14,7 @@ public final class Outer/Inner {
     public final @org.jetbrains.annotations.NotNull method getOuter(): Outer
 }
 
+@kotlin.Metadata
 public final class OuterThisKt {
     public final static @org.jetbrains.annotations.NotNull method box(): java.lang.String
 }