Merge pull request #2332 from jtattermusch/implicit_initialize_rebased

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

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

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

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

src/csharp/Grpc.Core/Calls.cs

src/csharp/Grpc.Core/Channel.cs

src/csharp/Grpc.Core/GrpcEnvironment.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/CompletionRegistry.cs

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

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

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

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

src/csharp/Grpc.Core/Server.cs

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

src/csharp/Grpc.Examples.MathServer/MathServer.cs

src/csharp/Grpc.Examples.Tests/MathClientServerTests.cs

src/csharp/Grpc.IntegrationTesting/InteropClient.cs