Remove Safari's support for tag and icon properties in the Notifications API

[captainbrosset]

Summary

Although Safari supports the tag and icon properties in the Notifications API, setting them doesn't do anything.

The icon property is supposed to allow developers to set an icon to be displayed in the system notification, replacing the default browser icon. But Safari doesn't actually display the icon.

The tag property is supposed to allow developers to avoid displaying too many notifications in a short amount of time. When developers use the same tag value, then new notifications replace old ones that haven't yet been displayed.
Safari doesn't seem to use tags, and sending bursts of same-tag notifications does still lead to multiple notifications being displayed to the user (although not all of them, but the logic seems UA-controlled, as opposed to based on the tag).

This PR therefore marks those 2 properties as not supported by Safari, with a note.

Test results and supporting details

Test page: https://patrickbrosset.com/lab/2024-09-26-notifications-with-icon-and-tag/

Here is a screenshot showing what notifications look like on Safari, even when an icon is specified:

And the same test, in Edge:

It's harder to show screenshots for the lack of tag support, but this webkit bug confirms it: https://webkit.org/b/258922
Especially this comment:

To be clear: the tag attribute on Notification is exposed. You can set it via the Notification constructor/ServiceWorkerRegistration.showNotification and access its value later on. But the browser currently doesn't use the property to coalesce notifications. That will require additional work.

[rejhgadellaa]

This shows that tag and icon is not working:

In the screenshots above, notice how on Android (left), there is one notification for each chatroom (two in total), which can be updated to include new messages. Each notification shows the profile picture of the sender. On the iPhone (right), instead of updating the existing notification, it creates a new one for each push message. They all have the same icon. Messages from Chatroom #1 are mixed with #2. None of these can be closed automatically by the web app, except the ones you tap.

https://webventures.rejh.nl/blog/2024/web-push-ios-one-year/#anchor--real-world-example

Btw, it also shows that badge isn't working either, but it is listed as supported on https://developer.mozilla.org/en-US/docs/Web/API/Notifications_API#browser_compatibility

Oh and thank you @captainbrosset !

[rejhgadellaa]

Ah, almost forgot. Related: #19318