do not generate protected constructors for enums (IDEA-53086)

java/java-tests/testData/codeInsight/generateConstructor/afterEnumWithAbstractMethod.java

@@ -0,0 +1,12 @@
+public enum Operation {
+    PLUS {
+        int eval(int x, int y) {
+            return x + y;
+        }
+    };
+
+    abstract int eval(int x, int y);
+
+    Operation() {
+    }
+}