Summary:
This commit update the React DevTools Flipper plugin to use the internal build of `react-devtools-core/standalone`.
The internal build of `react-devtools-core/standalone` is generated by the new sync script: `js1 upgrade react-devtools-core`, which places the build under `xplat/sonar/desktop/plugins/public/reactdevtools/fb`.
As a follow up, we can add a dropdown to allow users to select which version of React DevTools they'd like to use.
Reviewed By: mweststrate
Differential Revision: D31904288
fbshipit-source-id: ce0880284bd7f9ccaa6258a7c2956f20771e81a9