Move flow-typed definitions to repo root (#37636)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/37636

Moves `flow-typed/` directory from `packages/react-native/flow-typed/` to the repo root.

- This is a more suitable location for `flow-typed` definitions for 3P dependencies to be used across React Native packages.
- **Breaking**: We no longer publish these 3P libdefs as part of the `react-native` package (assuming that external use of React Native with Flow is extremely rare, and that these projects can manage their own package libdefs).

Changelog:
[General][Breaking] Remove included `flow-typed/` directory from the `react-native` package

- **Upgrade instructions**: Projects using Flow should install or replicate third party `flow-typed` definitions for React Native dependencies — see https://github.com/facebook/react-native/tree/main/flow-typed and [#37636](https://github.com/facebook/react-native/pull/37636).

Reviewed By: hoxyq

Differential Revision: D46313482

fbshipit-source-id: 3d97d5408e44dd43132664c4933f3ff1075f90a1