[5.7] Notifications can choose locale

[derekmd]

Follow-up to #23178 and #24451, this brings Notification localization behavior in line with Mailable. This allows notifications to choose their locale so when they're queued the subject line, greeting, body, etc. are always running as that locale instead of the app's default locale.

Notification::locale('es')->send(
    $users, new OrderConfirmation($order)
);

Auth::user()->notify(
    (new OrderConfirmation($order))->locale('es')
);

Multiple recipients for more than one language

I have a follow-up pull request to add a HasLocalePreference contract to users/notifiables so you can easily store user settings in the database and have Notification::send($users, new OrderConfirmation($order)); magically send the correct translation to each account.

The mailable-only preview is here: https://github.com/derekmd/framework/commits/mailable-localized-recipients

[taylorotwell]

@derekmd thanks. could you send a PR to docs (5.7 branch) to add this to the release notes with an explanation of how to use it?

[derekmd]

Sure, if not today I'll have something in by mid-week.