Summary: Move csharp tests into csharp/tests instead of tests. I feel like it makes more sense to have tests next to source. This is similar to how the C version has it as well.
Reviewed By: splhack
Differential Revision: D3993002
fbshipit-source-id: d9241f8ce7707c17a49c17fea2cce9959d52697d
871a7cf310