Infra: Bring `spectacle-mdx-loader` in to the monorepo

[ryan-roemer]

• [x] Add packages/spectacle-mdx-loader
• [x] Add examples/mdx that uses the loader
• [x] Remove old repository
• [ ] Verify we can correctly publish.

[paulmarsicloud]

Got a branch in progress for this: https://github.com/FormidableLabs/spectacle/tree/chore/spectacle-mdx-loader-addition 👍

[paulmarsicloud]

Revisited this branch today and I'm a little stuck. On a fresh pnpm install and pnpm start:mdx, http://localhost:3300/ blank screens with a external var "React":1 Uncaught ReferenceError: React is not defined

When I exit and re-run pnpm start:mdx, I get many Module not found: Error: Can't resolve 'react/jsx-runtime' errors even though the module is safely there.

Will continue to chip away at this

[Burnett2k]

Hi @ryan-roemer , I'm looking back at this and it appears that the old repo is still out there and might cause confusion. Should we archive / delete it to finish out this project? I see in the initial checklist removing the old repo was part of the issue. We probably need to also verify npm publishing works as well.

cc @carbonrobot

[ryan-roemer]

I think this is complete -- current version packages PR includes spectacle-mdx-loader. Plan sounds good -- verify npm publish, archive old repo. Thanks!