Added error 'NESTED_CLASS_SHOULD_BE_QUALIFIED'

when nested class is resolved through implicit this

compiler/testData/diagnostics/tests/inner/extensionFun.kt

@@ -23,6 +23,6 @@ class Outer {
 
 fun Outer.foo() {
     Outer()
-    <!NESTED_CLASS_ACCESSED_VIA_INSTANCE_REFERENCE!>Nested<!>()
+    <!NESTED_CLASS_SHOULD_BE_QUALIFIED!>Nested<!>()
     Inner()
 }

compiler/testData/diagnostics/testsWithStdLib/callableReference/function/nestedConstructorFromExtension.kt

@@ -6,7 +6,7 @@ class A {
 }
     
 fun A.main() {
-    ::<!NESTED_CLASS_ACCESSED_VIA_INSTANCE_REFERENCE!>Nested<!>
+    ::<!NESTED_CLASS_SHOULD_BE_QUALIFIED!>Nested<!>
     val y = A::Nested
     
     y : KFunction0<A.Nested>