Prohibit accessing nested classes/objects of class object using class literal

The fqname of class should be clear from code
Example: can't shorten A.Default.B.Default.C to A.B.C
Also fixes problem when nested class of enum class could be accessed via enum entry

compiler/testData/diagnostics/tests/classObjects/ClassObjectVisibility.kt

@@ -2,7 +2,7 @@ package foo
 
 fun test() {
   A.d
-  A.<!INVISIBLE_MEMBER!>f<!>
+  A.Default.<!INVISIBLE_MEMBER!>f<!>
   B.<!INVISIBLE_MEMBER!>D<!>
   <!INVISIBLE_MEMBER!>CCC<!>
   CCC.<!INVISIBLE_MEMBER!>classObjectVar<!>