docs: rename ng xi18n to ng extract-i18n (#39337)

In Angular CLI version 11, xi18n has been changed from `ng xi18n` to `ng extract-i18n`.

PR Close #39337

packages/compiler-cli/test/compliance/r3_view_compiler_i18n_spec.ts

@@ -41,7 +41,7 @@ const extract = (from: string, regex: any, transformFn: (match: any[], state: Se
 };
 
 // verify that we extracted all the necessary translations
-// and their ids match the ones extracted via 'ng xi18n'
+// and their ids match the ones extracted via 'ng extract-i18n'
 const verifyTranslationIds =
     (source: string, output: string, exceptions = {},
      interpolationConfig: InterpolationConfig = DEFAULT_INTERPOLATION_CONFIG) => {
@@ -2982,7 +2982,8 @@ describe('i18n support in the template compiler', () => {
       `;
 
       const exceptions = {
-        '3052001905251380936': 'Wrapper message generated by "ng xi18n" around ICU: "  {$ICU}  "'
+        '3052001905251380936':
+            'Wrapper message generated by "ng extract-i18n" around ICU: "  {$ICU}  "'
       };
       verify(input, output, {exceptions});
     });