[K/N] keep internal members in header klibs

This is also the behavior of jvm-abi-gen and desired to support
friend modules.
^KT-65442

native/native.tests/testData/klib/header-klibs/comparison/privateInterface/sameAbi/test.kt

@@ -1,7 +1,7 @@
 package test
 
 private interface A {
-    fun foo() = 42
+    fun foo(): Int { if (true) return 0 else return 1 }
     fun bar(): String
 }