Fix default projectRoot + watchFolders computation
Fix default projectRoot + watchFolders computation

Summary:
@public

This diff fixes the `projectRoot` calculation on React Native when the app does not have a config file. This should fix the issues reported in https://github.com/facebook/react-native/issues/20712

Reviewed By: hramos

Differential Revision: D9444982

fbshipit-source-id: 4cb41fa5224d2addf92976cc119e49dea6a6346b

hoangpham95/react-native,hammerandchisel/react-native,arthuralee/react-native,hammerandchisel/react-native,pandiaraj44/react-native,hammerandchisel/react-native,janicduplessis/react-native,pandiaraj44/react-native,myntra/react-native,arthuralee/react-native,hoangpham95/react-native,janicduplessis/react-native,exponent/react-native,arthuralee/react-native,exponent/react-native,facebook/react-native,exponent/react-native,exponent/react-native,facebook/react-native,janicduplessis/react-native,exponent/react-native,exponent/react-native,myntra/react-native,exponentjs/react-native,pandiaraj44/react-native,hammerandchisel/react-native,janicduplessis/react-native,javache/react-native,javache/react-native,myntra/react-native,javache/react-native,javache/react-native,hoangpham95/react-native,hoangpham95/react-native,exponent/react-native,hammerandchisel/react-native,arthuralee/react-native,facebook/react-native,myntra/react-native,exponentjs/react-native,hoangpham95/react-native,pandiaraj44/react-native,facebook/react-native,javache/react-native,exponentjs/react-native,exponentjs/react-native,javache/react-native,pandiaraj44/react-native,exponentjs/react-native,hoangpham95/react-native,hoangpham95/react-native,facebook/react-native,pandiaraj44/react-native,javache/react-native,janicduplessis/react-native,exponentjs/react-native,myntra/react-native,javache/react-native,hammerandchisel/react-native,arthuralee/react-native,exponentjs/react-native,javache/react-native,facebook/react-native,facebook/react-native,myntra/react-native,janicduplessis/react-native,pandiaraj44/react-native,pandiaraj44/react-native,myntra/react-native,facebook/react-native,exponentjs/react-native,hammerandchisel/react-native,hammerandchisel/react-native,janicduplessis/react-native,janicduplessis/react-native,facebook/react-native,myntra/react-native,hoangpham95/react-native,myntra/react-native,exponent/react-native