[Intl] Add feature mapping for Intl.DateTimeFormat-formatRange

Two PR of test262 tests are in
https://github.com/tc39/test262/pull/2139 and
https://github.com/tc39/test262/pull/2134

Bug: v8:7729
Change-Id: Ic416be0cec0fda90ee89c03ba4c6bb3192bf871d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1589633Reviewed-by: Jungshik Shin <jshin@chromium.org>
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Commit-Queue: Frank Tang <ftang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61144}

test/test262/testcfg.py

@@ -46,6 +46,7 @@ from testrunner.outproc import test262
 FEATURE_FLAGS = {
   'numeric-separator-literal': '--harmony-numeric-separator',
   'Intl.DateTimeFormat-datetimestyle': '--harmony-intl-datetime-style',
+  'Intl.DateTimeFormat-formatRange': '--harmony-intl-date-format-range',
   'Intl.Locale': '--harmony-locale',
   'Intl.Segmenter': '--harmony-intl-segmenter',
   'Symbol.prototype.description': '--harmony-symbol-description',