add C# server reflection

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

src/csharp/Grpc.Dotnet.sln

src/csharp/Grpc.Reflection.Tests/.gitignore

...csharp/Grpc.Reflection.Tests/Grpc.Reflection.Tests.csproj

.../Grpc.Reflection.Tests/Grpc.Reflection.Tests.project.json

src/csharp/Grpc.Reflection.Tests/Grpc.Reflection.Tests.xproj

src/csharp/Grpc.Reflection.Tests/NUnitMain.cs

src/csharp/Grpc.Reflection.Tests/Properties/AssemblyInfo.cs

...sharp/Grpc.Reflection.Tests/ReflectionClientServerTest.cs

src/csharp/Grpc.Reflection.Tests/SymbolRegistryTest.cs

src/csharp/Grpc.Reflection.Tests/packages.config

src/csharp/Grpc.Reflection.Tests/project.json

src/csharp/Grpc.Reflection/.gitignore

src/csharp/Grpc.Reflection/Grpc.Reflection.csproj

src/csharp/Grpc.Reflection/Grpc.Reflection.nuspec

src/csharp/Grpc.Reflection/Grpc.Reflection.project.json

src/csharp/Grpc.Reflection/Grpc.Reflection.xproj

src/csharp/Grpc.Reflection/Properties/AssemblyInfo.cs

src/csharp/Grpc.Reflection/Reflection.cs

src/csharp/Grpc.Reflection/ReflectionGrpc.cs