Cleanup test cases to remove the dependency on ProtoGeometry.dll

These test cases are marked as Ignored. Replace test library with ``FFITarget.dll`` and re-enable them.

Also deriving ``CSFFITest`` from ``ProtoTestBase``. 

@sharadkjaiswal  for your review.  
We would like to get rid of usage of ExecutionMirror and replace with RuntimMirror wherever possible. I guess thisTest.Verify should have worked. No need to use mirror.