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/objects/invokeOnInnerObject.kt

@@ -1,6 +1,6 @@
 //no nested class access via instance reference error
 fun test() {
-    A.f(<!TYPE_MISMATCH!>""<!>)
+    A.Default.f(<!TYPE_MISMATCH!>""<!>)
 }
 
 class A() {