Handle request errors on useUser hook [SDK-3227]

[Widcket]

Description

This PR handles errors thrown in the user fetcher and exposes them through the error property of the useUser hook. This means that, for example, the user going offline will not cause the checkSession() function to clear the user property of the useUser hook, but instead, the developer will get a RequestError with a status value of 0 in the error property:

Screen.Recording.2022-04-06.at.20.16.08.mov

This also means that developers can throw their own errors in their custom fetchers, and get them via the useUser hook.

Testing

• [ X] This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not main

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