Extraction Engine: Report invisible types in the generated declaration header

#KT-6734 Fixed

idea/testData/refactoring/extractFunction/basic/invisibleType.kt

@@ -0,0 +1,11 @@
+// SIBLING:
+class A {
+    private class Inner {
+        fun foo() {}
+    }
+
+    fun foo() {
+        val inner = Inner()
+        <selection>inner.foo()</selection>
+    }
+}

idea/testData/refactoring/extractFunction/basic/invisibleType.kt.conflicts

@@ -0,0 +1 @@
+Class A.Inner will become invisible after extraction