Summary:
I put the CMake file in the root directory to avoid moving the actual `yoga/`
dir around, but created a directory for the Android library manifest nonsense
so it works as its own module you can depend on.
Reviewed By: emilsjolander
Differential Revision: D4913601
fbshipit-source-id: 582064264cf0b6b69c03d0e72ed9dd22d217dd16
