Summary: Update `react-devtools-core` and `react-devtools` dependencies for RN, VSCode, Flippe, etc. `js1 upgrade react-devtools -v 4.21.0` # Changelog: [General][Changed] - Upgraded react-devtools-core dependency to 4.21.0 Reviewed By: bvaughn Differential Revision: D32065685 fbshipit-source-id: 30d0cca2bec6e9abe384da2afefab1d241e0523f