Support bs-platform@7

The problem

Is bs-platform@7.0.1 on the roadmap?

Considered solution

I started the conversion here: https://github.com/idkjs/reason-react-native/tree/bs_platform_701

Tested on the template here: https://github.com/idkjs/reason-react-native-bs701

Of note, I have not completed VirtualizedList.re yet since there is some trickery with section in that file.

I also have not converted the .md's yet. I wanted to get some feedback before continuing.

All of the changes are to implement the new syntax. A few examples are:

registry
photoIdentifier
layoutEvent

How do you test this repo? Is there a way to find out if I have broken anything?

Should I make a pull request?