feat(ivy): allow the locale to be set via a global property (#33314)

In the post-$localize world the current locale value is defined by setting
`$localize.locale` which is then read at runtime by Angular in the provider
for the `LOCALE_ID` token and also passed to the ivy machinery via`setLocaleId()`.

The $localize compile-time inlining tooling can replace occurrences of
`$localize.locale` with a string literal, similar to how translations
are inlined.

// FW-1639

See https://github.com/angular/angular-cli/issues/15896

PR Close #33314

packages/localize/src/localize/src/localize.ts

@@ -20,6 +20,22 @@ export interface LocalizeFn {
    * different translations.
    */
   translate?: TranslateFn;
+  /**
+   * The current locale of the translated messages.
+   * 
+   * The compile-time translation inliner is able to replace the following code:
+   * 
+   * ```
+   * $localize && $localize.locale
+   * ```
+   * 
+   * with a string literal of the current locale. E.g.
+   * 
+   * ```
+   * "fr"
+   * ```
+   */
+  locale?: string;
 }
 
 export interface TranslateFn {