fixed writeOptions and added test

src/csharp/Grpc.Core.Tests/CompressionTest.cs

src/csharp/Grpc.Core.Tests/Grpc.Core.Tests.csproj

src/csharp/Grpc.Core/CallOptions.cs

src/csharp/Grpc.Core/IAsyncStreamWriter.cs

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

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

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

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

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

src/csharp/ext/grpc_csharp_ext.c