Used StyleCop to get rid of tabs in the source code

src/csharp/.gitignore

src/csharp/Grpc.Core/Internal/CallSafeHandle.cs

...csharp/Grpc.Core/Internal/ClientStreamingInputObserver.cs

src/csharp/Grpc.Core/Internal/CompletionQueueSafeHandle.cs

...sharp/Grpc.Core/Internal/ServerStreamingOutputObserver.cs

src/csharp/Grpc.Core/Internal/Timespec.cs

src/csharp/Grpc.Core/Status.cs

src/csharp/Grpc.Examples.MathClient/MathClient.cs

src/csharp/Grpc.Examples/MathExamples.cs