Assert that reference annotation argument is always an enum value

Rename JavaReferenceAnnotationArgument on that occasion to
JavaEnumValueAnnotationArgument. Also add a test on a nested enum annotation
argument

compiler/testData/loadJava/compiledJava/annotations/NestedEnumArgument.java

@@ -0,0 +1,14 @@
+package test;
+
+public class NestedEnumArgument {
+    public enum E {
+        FIRST
+    }
+
+    @interface Anno {
+        E value();
+    }
+
+    @Anno(E.FIRST)
+    void foo() {}
+}