Add missing i18n types in gip context (vercel#25363)

## Bug

- [x] Related issues linked using `fixes #number`
- [ ] Integration tests added

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.

## Documentation / Examples

- [] Make sure the linting passes

Ref: vercel#21930

packages/next/next-server/lib/utils.ts

@@ -135,6 +135,18 @@ export interface NextPageContext {
    * `String` of the actual path including query.
    */
   asPath?: string
+  /**
+   * The currently active locale
+   */
+  locale?: string
+  /**
+   * All configured locales
+   */
+  locales?: string[]
+  /**
+   * The configured default locale
+   */
+  defaultLocale?: string
   /**
    * `Component` the tree of the App to use if needing to render separately
    */