new integration: stylex

[lilnasy]

Changes

• A build-time CSS-in-JS library.
• Built direcly on top of the babel plugin.
• Not using the rollup plugin because it seemed rushed.

Testing

• Added dev and build tests for react.
• The rest can wait while StyleX gets fleshed out.

Docs

Pending

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Latest commit: 460419eeb6fb3b8c13d79a94d878192f029378a1

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