NuGet package Grpc.HealthCheck Version 2.28.1 does not compile .NET 4.5 lib with #define GRPC_SUPPORT_WATCH

[andrekoehler]

https://github.com/grpc/grpc/blob/v1.28.1/src/csharp/Grpc.HealthCheck/HealthServiceImpl.cs#L134

Decompiler output of

"C:\Users\andre\.nuget\packages\grpc.healthcheck\2.28.1\lib\net45\Grpc.HealthCheck.dll" shows that class "Grpc.HealthCheck.HealthServiceImpl" does not implement the Watch method, but
"C:\Users\andre\.nuget\packages\grpc.healthcheck\2.28.1\lib\net462\Grpc.HealthCheck.dll" does implement it!

I noticed this because I upgraded the Grpc.HealthCheck package in my .NET 4.5 hoping that I would get the implementation of the Watch method, but my client still returned error code UNIMPLEMENTED when calling the watch method.

[jtattermusch]

The watch implementation is currently only supported for net462 and netstandard2.0.
https://github.com/grpc/grpc/pull/21120/files#diff-8a3c5313f31d458cd763e3da44471824R22

I'd recommend migrating to one the newer frameworks of them to benefit from all the new features. (an actual net45 is very very old).