feat(ivy): use i18n locale data to determine the plural form of ICU expressions (#29249)

Plural ICU expressions depend on the locale (different languages have different plural forms). Until now the locale was hard coded as `en-US`.
For compatibility reasons, if you use ivy with AOT and bootstrap your app with `bootstrapModule` then the `LOCALE_ID` token will be set automatically for ivy, which is then used to get the correct plural form.
If you use JIT, you need to define the `LOCALE_ID` provider on the module that you bootstrap.
For `TestBed` you can use either `configureTestingModule` or `overrideProvider` to define that provider.
If you don't use the compat mode and start your app with `renderComponent` you need to call `ɵsetLocaleId` manually to define the `LOCALE_ID` before bootstrap. We expect this to change once we start adding the new i18n APIs, so don't rely on this function (there's a reason why it's a private export).
PR Close #29249

packages/core/src/render3/index.ts

@@ -100,6 +100,7 @@ export {
 } from './state';
 
 export {
+  DEFAULT_LOCALE_ID,
   ɵɵi18n,
   ɵɵi18nAttributes,
   ɵɵi18nExp,
@@ -109,6 +110,8 @@ export {
   ɵɵi18nPostprocess,
   i18nConfigureLocalize,
   ɵɵi18nLocalize,
+  getLocaleId,
+  setLocaleId,
 } from './i18n';
 
 export {NgModuleFactory, NgModuleRef, NgModuleType} from './ng_module_ref';