Add the Enum default method getInternalStringValue() when "has_int_str_val" is set (TODO: Query this using XPath, fdik how do i do this? in ysl2?)

src/codegen/gen_java_Message.ysl2

@@ -136,9 +136,20 @@ tstylesheet {
                 }
                 return null;
             }
-        }
 
         ||
+        choose {
+            when "@has_int_str_val = 'true'" {
+            ||
+                public String getInternalStringValue() {
+                    return "Unimplemented";
+                }
+            ||
+            }
+        }
+        ||
+        }
+        ||
     }
 
     function "exception" {

src/codegen/pEp.yml2

@@ -24,7 +24,7 @@ namespace pEp {
     };
 
 
-    enum Rating {
+    enum has_int_str_val=true Rating {
        enumitem pEp_rating_undefined              int_str_val=undefined                toString="undefined"               > 0
        enumitem pEp_rating_cannot_decrypt         int_str_val=cannot_decrypt           toString="cannot decrypt"          > 1
        enumitem pEp_rating_have_no_key            int_str_val=have_no_key              toString="have no key"             > 2