An implementation of KT-7753: now enum constructors cannot be called explicitly.

Several tests are provided.
 #KT-7753 Fixed.

compiler/testData/diagnostics/tests/enum/InsideEntryConstructorCall.kt

@@ -0,0 +1,15 @@
+// KT-7753: attempt to call enum constructor explicitly
+enum class A(val c: Int) {
+    ONE(1) {
+        override fun selfOrFriend(): A {
+            return this
+        }
+    },
+    TWO(2) {
+        override fun selfOrFriend(): A {
+            return <!ENUM_CLASS_CONSTRUCTOR_CALL!>A(42)<!>
+        }
+    };
+    
+    abstract fun selfOrFriend(): A
+}