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/codegen/box/enum/inclassobj.kt

@@ -1,4 +1,4 @@
-fun box() = if(Context.operatingSystemType == Context.OsType.OTHER) "OK" else "fail"
+fun box() = if(Context.operatingSystemType == Context.Default.OsType.OTHER) "OK" else "fail"
 
 public class Context
 {