Expose box sizing getters and setters in Yoga (#46630)

Summary:
X-link: https://github.com/facebook/yoga/pull/1701

Pull Request resolved: https://github.com/facebook/react-native/pull/46630

I would like to write some tests for box sizing that will drive a lot of my development as I implement content box. To do that, I need this publicly exposed. Obviously not that ideal since this currently does not do anything. Maybe we can name the value in such a way that its clear it is in development?

Changelog: [Internal]

Reviewed By: NickGerleman

Differential Revision: D63135970

fbshipit-source-id: 7520823bf925364eae45341531e012e80ec92284