This has one important benefit: fixing the stretching behavior of spacer nodes.
In addition, it should help efficiency of Yoga and certainly minimize calls
to layoutThatFits:.
Next up for Yoga is a mostly-red diff, deleting the non-Contiguous code branches.
* no message
* Go further
* Make the symbols public so that apps actually build
* Move ASAvailability into the umbrella header
* Remove duplicate define
* Put the file back where it was in the list
* Revert "Put the file back where it was in the list"
This reverts commit 6a80c15b5b5efe5ff39812a018114e8bdc1dc0cf.
