Fix Intl to clear needDefault flag correctly (#1014)

Summary:
Similar to year, month, and day, specifying "weekday" as an option to
`toLocaleString` should result in only the weekday being printed. To
force this, use the `kDateRequired` bit as we do for the other fields.

Pull Request resolved: #1014

Test Plan: Added a test in the next diff.

Reviewed By: tmikov

Differential Revision: D49856174

Pulled By: neildhar

fbshipit-source-id: ed52f425e4240f672931d236bc53cc58724b6747

lib/VM/JSLib/Intl.cpp

@@ -269,7 +269,7 @@ constexpr OptionData kDTFOptions[] = {
     {u"hourCycle", platform_intl::Option::Kind::String, 0},
     {u"timeZone", platform_intl::Option::Kind::String, 0},
     {u"formatMatcher", platform_intl::Option::Kind::String, 0},
-    {u"weekday", platform_intl::Option::Kind::String, 0},
+    {u"weekday", platform_intl::Option::Kind::String, kDateRequired},
     {u"era", platform_intl::Option::Kind::String, 0},
     {u"year",
      platform_intl::Option::Kind::String,