Inject Intl polyfills where used (#20798)

* Inject Intl polyfills where used

* Replace Intl polyfill in localize method with loading intl-messageformat asynchronously

* Remove spurious feature tests for Intl

build-scripts/babel-plugins/custom-polyfill-plugin.js

@@ -29,6 +29,31 @@ const PolyfillSupport = {
     safari: 10.1,
     samsung: 4.0,
   },
+  "intl-getcanonicallocales": {
+    android: 54,
+    chrome: 54,
+    edge: 16,
+    firefox: 48,
+    ios: 10.3,
+    opera: 41,
+    opera_mobile: 41,
+    safari: 10.1,
+    samsung: 6.0,
+  },
+  "intl-locale": {
+    android: 74,
+    chrome: 74,
+    edge: 79,
+    firefox: 75,
+    ios: 14.0,
+    opera: 62,
+    opera_mobile: 53,
+    safari: 14.0,
+    samsung: 11.0,
+  },
+  "intl-other": {
+    // Not specified (i.e. always try polyfill) since compatibility depends on supported locales
+  },
   proxy: {
     android: 49,
     chrome: 49,
@@ -70,7 +95,31 @@ const polyfillMap = {
       module: "element-internals-polyfill",
     },
   },
-  static: {},
+  static: {
+    Intl: {
+      getCanonicalLocales: {
+        key: "intl-getcanonicallocales",
+        module: join(POLYFILL_DIR, "intl-polyfill.ts"),
+      },
+      Locale: {
+        key: "intl-locale",
+        module: join(POLYFILL_DIR, "intl-polyfill.ts"),
+      },
+      ...Object.fromEntries(
+        [
+          "DateTimeFormat",
+          "DisplayNames",
+          "ListFormat",
+          "NumberFormat",
+          "PluralRules",
+          "RelativeTimeFormat",
+        ].map((obj) => [
+          obj,
+          { key: "intl-other", module: join(POLYFILL_DIR, "intl-polyfill.ts") },
+        ])
+      ),
+    },
+  },
 };
 
 // Create plugin using the same factory as for CoreJS