Summary:
This commit makes both `:ReactAndroid` and `:rn-tester:android:app` always compile in Fabric codegen outputs. However, one may still enable/disable Fabric at runtime by setting `USE_FABRIC` env var (set to 1 or 0, default is 0).
Note that we can't register custom components specific to the app, yet, so only the components in react-native github repo is covered by this commit.
RNTester doesn't enable Fabric by default yet due to known UI bugs that haven't been addressed yet.
Changelog: [Internal]
Reviewed By: mdvacca
Differential Revision: D25674311
fbshipit-source-id: 8db660c959319250ebc683c84076677cf6489e94