Allow modifier 'inner' on a class nested in enum entry class

compiler/testData/diagnostics/tests/inner/innerClassInEnumEntryClass_lv12.kt

@@ -0,0 +1,19 @@
+// !LANGUAGE: +InnerClassInEnumEntryClass
+
+enum class Enum {
+    ENTRY_WITH_CLASS {
+        inner class TestInner
+
+        class TestNested
+
+        interface TestInterface
+
+        object TestObject
+
+        enum class TestEnumClass {
+            OTHER_ENTRY
+        }
+
+        <!WRONG_MODIFIER_CONTAINING_DECLARATION!>companion<!> object {}
+    }
+}