Report 'nested class accessed via instance reference' error

idea/testData/diagnosticMessage/nestedClassAcessedViaInstanceReference.kt

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+// !DIAGNOSTICS_NUMBER: 4
+// !DIAGNOSTICS: NESTED_CLASS_ACCESSED_VIA_INSTANCE_REFERENCE
+
+class A {
+    class Nested()
+    class NestedWithClassObject { class object }
+    enum class NestedEnum { A }
+    object NestedObj { fun invoke() = 1 }
+}
+
+fun test(a: A) {
+    a.Nested()
+    a.NestedWithClassObject
+    a.NestedEnum
+    a.NestedObj
+}

idea/testData/diagnosticMessage/nestedClassAcessedViaInstanceReference1.txt

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+<!-- nestedClassAcessedViaInstanceReference1 -->
+Nested class 'Nested' accessed via instance reference

idea/testData/diagnosticMessage/nestedClassAcessedViaInstanceReference2.txt

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+<!-- nestedClassAcessedViaInstanceReference2 -->
+Nested class object of 'NestedWithClassObject' accessed via instance reference

idea/testData/diagnosticMessage/nestedClassAcessedViaInstanceReference3.txt

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+<!-- nestedClassAcessedViaInstanceReference3 -->
+Nested enum class 'NestedEnum' accessed via instance reference

idea/testData/diagnosticMessage/nestedClassAcessedViaInstanceReference4.txt

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+<!-- nestedClassAcessedViaInstanceReference4 -->
+Nested object 'NestedObj' accessed via instance reference