Summary:
Added a subset of the global flow types from the fbjs eslint config to remove the no-undef errors for flow types as well as a few missing browser globals that were used in the codebase.

I also added a .eslintrc file to Examples to allow using alert there without warnings.
Closes https://github.com/facebook/react-native/pull/5585

Reviewed By: svcscm

Differential Revision: D2872016

Pulled By: vjeux

fb-gh-sync-id: f9b1b511289425393074b7237049dec38ea407b6