Summary:
In most .gradle files, lines are indented with 4 spaces, but in some places they are indented with 2 spaces. This PR fixes them and enforce it by adding .editorconfig settings.
Closes https://github.com/facebook/react-native/pull/10267
Differential Revision: D4048335
Pulled By: lacker
fbshipit-source-id: df2f2556380f56672cf85690eb1c80e640a6aedf