Add TypeScript guides

[gitKrystan]

While we have grand plans to eventually have a js/ts toggle for all of the guides, we need something to point to in the meantime. In this PR, I am adding initial TypeScript guides pulled from the various resources currently scattered across the interwebs to use as a starting point.

These pages currently will not show up in the table of contents. You'll have to visit the link directly. The purpose of this is to allow us to merge this mega-PR and continue to iterate without being fully released. In the meantime, we can link people directly to these pages with the caveat that the pages are still under construction.

Sources:

• https://docs.ember-cli-typescript.com/
• https://blog.skylight.io/ts-extends-confidence-2-2022/

This will help us close out emberjs/rfcs#952

To review:

Visit deploy preview linked below and navigate to ./release/using-typescript/
(e.g. https://deploy-preview-1960--ember-guides.netlify.app/release/using-typescript/ for the deploy that was current at the time of this writing)

Review for:

• Typos
• Mistakes
• Completeness

Please make liberal use of the GitHub suggestions feature because I am starting to get bleary-eyed looking at this for so long. 🙏

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[chriskrycho]

Thanks for getting this started! I left a bunch of suggestions, and I think we want to keep these out of the top-level outline for now, but getting it started this way is awesome, and now we can iterate!

[gitKrystan]

Lint should be fixed now.

I played w/ moving the chapter up a level (per discussion on Discord) and it makes the initial TOC super long + pushes some of the TypeScript chapters to the same level as their top-level equivalent (e.g. "Getting Started" at the same level as "TypeScript: Getting Started") which I found a bit confusing.

I also played with splitting up the Invokables chapter and there wasn't a great place to split it (it's written as one narrative that references itself a lot), so I left it as is.

[mansona]

LGTM 💪