Extract Function: Check for INVISIBLE_* errors during validation phase

#KT-4995 Fixed

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

@@ -0,0 +1,7 @@
+// SIBLING:
+public class A {
+    private class B
+    fun f() {
+        <selection>val b: A.B</selection>
+    }
+}