Summary:
We still need to wait for the `YGUnitPoint` PR to be merged :) But please let me know what you think. One caveat: because of a limitation of Swift, a literal value can be automatically understood as a point-based `YGValue`, but variables have to be explicitly cast. I haven't found a way around it yet:
```
view.yoga.width = 10 // value == 10, unit == YGUnitPixel
let a: CGFloat = 100
view.yoga.height = a // Compiler error
view.yoga.height = YGValue(a) // works, not great
```
Closes https://github.com/facebook/yoga/pull/390
Reviewed By: emilsjolander
Differential Revision: D4954021
Pulled By: maxoll
fbshipit-source-id: 5eff6aeb6dd969d0d5dc557b149bb5819b0e31de
7b89a1dd48