Enum entries: add new tests with language feature ON & fix checker

compiler/testData/diagnostics/tests/enum/entries/nameShadowingOfExternallyDefinedEntriesOn.kt

@@ -0,0 +1,40 @@
+// !LANGUAGE: +EnumEntries
+// WITH_STDLIB
+
+package pckg
+
+val entries = "E"
+
+enum class E {
+    ;
+
+    fun foo() {
+        <!DEPRECATED_ACCESS_TO_ENTRY_PROPERTY_FROM_ENUM!>entries<!>.length
+        pckg.entries.length
+    }
+}
+
+class A {
+    enum class E {
+        ;
+
+        class B {
+            fun foo() {
+                <!DEPRECATED_ACCESS_TO_ENTRY_PROPERTY_FROM_ENUM!>entries<!>.length
+                pckg.entries.length
+            }
+        }
+
+        class C {
+            val entries = 0
+
+            fun foo() {
+                // technically, this warning is incorrect but I believe it's OK to report anyway
+                // first, logic in the compiler will be complicated if we'll try to avoid reporting warnings here
+                // second, this code smells,  it'd be better to use qualifiers here anyway
+                <!DEPRECATED_ACCESS_TO_ENTRY_PROPERTY_FROM_ENUM!>entries<!> + 4
+                this.entries + 4
+            }
+        }
+    }
+}