Handle updating es2020.intl and add es2021 for new DateTimeFormatOptions options - re: microsoft#39664

Author: orta

lib/lib.es2021.d.ts

@@ -22,3 +22,4 @@ and limitations under the License.
 /// <reference lib="es2021.promise" />
 /// <reference lib="es2021.string" />
 /// <reference lib="es2021.weakref" />
+/// <reference lib="es2021.intl" />

src/lib/es2020.intl.d.ts

@@ -13,16 +13,22 @@ declare namespace Intl {
      * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/format#Parameters).
      */
     type RelativeTimeFormatUnit =
-        | "year" | "years"
-        | "quarter" | "quarters"
-        | "month" | "months"
-        | "week" | "weeks"
-        | "day" | "days"
-        | "hour" | "hours"
-        | "minute" | "minutes"
-        | "second" | "seconds"
-        ;
-
+        | "year"
+        | "years"
+        | "quarter"
+        | "quarters"
+        | "month"
+        | "months"
+        | "week"
+        | "weeks"
+        | "day"
+        | "days"
+        | "hour"
+        | "hours"
+        | "minute"
+        | "minutes"
+        | "second"
+        | "seconds";
     /**
      * The locale matching algorithm to use.
      *

src/lib/es2021.intl.d.ts

@@ -0,0 +1,9 @@
+declare namespace Intl {
+
+    interface DateTimeFormatOptions {
+        dateStyle?: "full" | "long" | "medium" | "short";
+        timeStyle?: "full" | "long" | "medium" | "short";
+        dayPeriod?: "narrow" | "short" | "long";
+        fractionalSecondDigits?: 0 | 1 | 2 | 3;
+    }
+}

src/lib/libs.json

@@ -51,6 +51,7 @@
         "es2021.string",
         "es2021.promise",
         "es2021.weakref",
+        "es2021.intl",
         "esnext.intl",
         // Default libraries
         "es5.full",