[klibs] header klibs should keep private interfaces

^KT-62213 Fixed

native/native.tests/testData/klib/header-klibs/compilation/classes/lib/classes.kt

@@ -5,7 +5,11 @@ interface I {
     fun iMethod(): Int
 }
 
-open class A : I {
+private interface K {
+    fun kMethod() = 42
+}
+
+open class A : I, K {
     override val iProperty: Int = 0
     override fun iMethod(): Int = 10
 

native/native.tests/testData/klib/header-klibs/compilation/classes/main/main.kt

@@ -7,6 +7,10 @@ fun useI(i: I) {
     i.iMethod()
 }
 
+fun useK(k: A) {
+    k.kMethod()
+}
+
 fun useA(a: A) {
     a.iProperty
     a.iMethod()
@@ -37,6 +41,7 @@ fun useC(b: String) {
 
 fun runAppAndReturnOk(): String {
     useI(A())
+    useK(A())
     useA(A())
     useB(B())
     useC("test")