Summary: Wires C ABI to C# bindings using `System.Runtime.InteropServices`. Note that we don't have a working C# build right now, but there is [effort to address that](https://github.com/facebook/yoga/pull/1207) which may get some more effort before the Yoga release, so this keeps the bindings up to date.
Differential Revision: https://internalfb.com/D45297676
fbshipit-source-id: 07ca3b5c0509f18ad825029804b68ccb5c4e5522
fbdd86c188