Allow general language codes in the Metadata API (#52920)

Closes #52898

LangCode Missing zh-Hans and zh-Hant

| 'yo-NG'
  | 'zh-CN'
  | 'zh-Hans'   //added
  | 'zh-Hant'        //added
  | 'zh-HK'
  | 'zh-MO'
  | 'zh-SG'
  | 'zh-TW'
  | 'zu-ZA'


https://github.com/vercel/next.js/blob/f5272acbe5628164257ef8e584c8a469a4af5cb8/packages/next/src/lib/metadata/types/alternative-urls-types.ts#L419


Co-authored-by: Shu Ding <3676859+shuding@users.noreply.github.com>

packages/next/src/lib/metadata/resolvers/resolve-basics.ts

@@ -66,7 +66,10 @@ export const resolveViewport: FieldResolver<'viewport'> = (viewport) => {
 
 function resolveUrlValuesOfObject(
   obj:
-    | Record<string, string | URL | AlternateLinkDescriptor[] | null>
+    | Record<
+        string,
+        string | URL | AlternateLinkDescriptor[] | null | undefined
+      >
     | null
     | undefined,
   metadataBase: ResolvedMetadata['metadataBase'],

packages/next/src/lib/metadata/types/alternative-urls-types.ts

@@ -412,7 +412,15 @@ type LangCode =
   | 'zh-MO'
   | 'zh-SG'
   | 'zh-TW'
+  | 'zh-Hans'
+  | 'zh-Hant'
   | 'zu-ZA'
+  // We can't have all valid combinations of language-region-script listed here
+  // as the list is too long and breaks the TypeScript compiler. So instead we
+  // only add the most common ones with a general string pattern for the rest.
+  // This way autocompletion still works and it is still possible to add custom
+  // lang codes.
+  | `${Lowercase<string>}-${string}`
 
 type UnmatchedLang = 'x-default'