Fix enum entry reference from enum entry initialization context

Enum entries are "special" kind of singletons that should be
referenced as a captured 'this' instance inside during entry
initialization, because corresponding static fields in enum class
are not initialized yet.

 #KT-7257 Fixed

compiler/testData/codegen/box/enum/kt7257_boundReferenceWithImplicitReceiver.kt

@@ -0,0 +1,16 @@
+// LANGUAGE_VERSION: 1.2
+// IGNORE_BACKEND: JS
+
+enum class X {
+    B {
+        override val value = "OK"
+
+        override val test = ::value.get()
+    };
+
+    abstract val value: String
+
+    abstract val test: String
+}
+
+fun box() = X.B.test