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

tools/public_api_guard/common/common.d.ts

@@ -103,7 +103,7 @@ export declare function getLocaleNumberFormat(locale: string, type: NumberFormat
 
 export declare function getLocaleNumberSymbol(locale: string, symbol: NumberSymbol): string;
 
-export declare function getLocalePluralCase(locale: string): (value: number) => Plural;
+export declare const getLocalePluralCase: (locale: string) => ((value: number) => Plural);
 
 export declare function getLocaleTimeFormat(locale: string, width: FormatWidth): string;