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

Several tests are provided.
 #KT-7753 Fixed.

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

@@ -0,0 +1,10 @@
+// KT-7753: attempt to call enum constructor explicitly
+enum class A(val c: Int) {
+    ONE(1),
+    TWO(2);
+    
+    fun createA(): A {
+        // Error should be here!
+        return <!ENUM_CLASS_CONSTRUCTOR_CALL!>A(10)<!>
+    }
+}