[DRAFT] Revamp "Redux Essentials" tutorial to be TS-first and update contents

[markerikson]

Actual content changes for #4393 , at long last!

The current WIP example code is over in:

• https://github.com/reduxjs/redux-essentials-example-app/tree/feature/tutorial-steps-ts-revamped

I'm doing another round of revisions and step-by-step checking to those code commits as I rework the tutorial content, but that should be the progression and code content I want to show off in the tutorial.

Big picture summary:

• The entire example app is TS, start to finish
• Improve some existing explanations
• Cover some concepts that weren't included originally, like having multiple reducers handle one action
• Cover newer APIs we didn't have in 2020, like createListenerMiddleware and thunks in createSlice
• While not Redux-related, update some of the usage patterns like React Router 5 -> 6 and using uncontrolled inputs in forms instead of controlled

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