* Eliminates the server mutating the a `WP_Error`'s `$error_data` to merge-in a `$from_server` flag (since it may not be an array to begin with). Instead it defers to the client to add a `fromServer` param on any `Notification` instances created from server-sent errors.
* Ensures that notifications will be re-rendered if a notification's `message` changes but the `data` and `type` remain the same.
* Adds explicit support for the `Notification` class to have a `setting` property, ensuring that the property is set whereas previously it was dropped.
Fixes#37890.
Props westonruter, dlh.
git-svn-id: https://develop.svn.wordpress.org/trunk@38513 602fd350-edb4-49c9-b593-d223f7449a82
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