Update ECOSYSTEM.md to reflect updated partnerships (#29527)

Summary:
To help reflect how we've collectively been thinking about partnership and engagement on React Native, this change moves Facebook into the Partners list alongside other partners like Expo, Microsoft, and others. This change helps establish that the React Native teams across Facebook & Microsoft are one big happy family :)

## Changelog

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[General] [Changed] - Updated ECOSYSTEM.md to reflect partnerships between Facebook, Microsoft, and others

Pull Request resolved: https://github.com/facebook/react-native/pull/29527

Test Plan: N/A - document change

Reviewed By: cpojer

Differential Revision: D22845420

Pulled By: TheSavior

fbshipit-source-id: b3393c8749efc924b27d101d0513ae55eba55270