fix(compiler-cli): adding missing format xliff for the extractor (ang…

…ular#15386)

To generate XLF files with ng-xi18n we could use the format parameter "xlf" or "xlif". The real name is "xliff" not "xlif", so this probably was a typo. This PR adds "xliff" as can be expected

packages/compiler-cli/src/extractor.ts

@@ -67,7 +67,7 @@ export class Extractor {
     const format = (formatName || 'xlf').toLowerCase();
 
     if (format === 'xmb') return 'xmb';
-    if (format === 'xlf' || format === 'xlif') return 'xlf';
+    if (format === 'xlf' || format === 'xlif' || format === 'xliff') return 'xlf';
 
     throw new Error('Unsupported format "${formatName}"');
   }