Add feature for well-formed-stringify tests

features.txt

@@ -99,6 +99,10 @@ Symbol.prototype.description
 # https://github.com/tc39/proposal-json-superset
 json-superset
 
+# Well-formed JSON.stringify
+# https://github.com/tc39/proposal-well-formed-stringify
+well-formed-json-stringify
+
 # Intl.ListFormat
 # https://github.com/tc39/proposal-intl-list-format
 Intl.ListFormat

test/built-ins/JSON/stringify/string-escape-unicode.js

@@ -5,6 +5,7 @@
 esid: sec-quotejsonstring
 description: >
     JSON.stringify strings containing surrogate code units
+features: [well-formed-json-stringify]
 ---*/
 
 assert.sameValue(JSON.stringify("\uD834"), '"\\ud834"',