feat(react-scripts): support CSS in JS via Linaria

[jednano]

Fixes #5224

Introduces Linaria as the way to support CSS in JS, because it's the most feature rich option (including TypeScript support).

See this comment for the value proposition.

I got this working in my local dev environment by making these changes directly in my node_modules/react-scripts folder. I followed up with npm run build to see if it worked there too and there were no visible issues. A screenshot would be useless, because it looks exactly the same as a standard CRA home page.

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[jednano]

For anyone interested, I introduced Linaria without ejecting in this commit.