Support getSnapshotBeforeUpdate for shallow

[koba04]

Current behavior

React v16.3.0 introduced new lifecycle method called getSnapshotBeforeUpdate.
the method isn't supported by ShallowRenderer so we have to add support the method on enzyme if needed.
The method is called at the same timing with componentWillUpdate so we might need some hacks ShallowRenderer internals.
In addition to that, the arguments of componentDidUpdate have been changed, which accepts snapshot as the 3rd argument.

https://reactjs.org/blog/2018/03/27/update-on-async-rendering.html

Should enzyme support this method?
If so, I'd like to work on based on #1192

Expected behavior

Your environment

API

• shallow
• mount
• render

Version

library	version
Enzyme	3.3.0
React	16.3.0

Adapter

• enzyme-adapter-react-16
• enzyme-adapter-react-15
• enzyme-adapter-react-15.4
• enzyme-adapter-react-14
• enzyme-adapter-react-13
• enzyme-adapter-react-helper
• others ( )

[tennisgent]

Yes please 👍