Support react-native-fs for RNW vNext

[namrog84]

Cannot read property 'RNFSFileTypeRegular' of undefined

react-native-fs has a RNFSManager which has some constants and other fairly low level stuff.
There is a /windows module but it is using cs and is designed for RNWcurrent and so RNWvNext and it's use of 'uwp' makes this not work.

https://github.com/itinance/react-native-fs/tree/master/windows/RNFS

Also rn-fetch-blob doesn't have windows support. And it is sorta related to file system things.
https://github.com/joltup/rn-fetch-blob

[harinikmsft]

Thanks for trying this out. We are currently in the middle of providing the native modules/view managers story for targeting RNW-vnext. So, any of the community modules that need this story will not currently support RNW-vnext yet. Once this story is ready, we would love to get some help making these community modules work against RNW -vnext.

Stay tuned for updates!