protobuf-net.Grpc

What's Changed

• Implement initial Stream API support by @mgravell in https://github.com/protobuf-net/protobuf-net.Grpc/pull/341
  • (and fix initial memory recycling error, https://github.com/protobuf-net/protobuf-net.Grpc/pull/342)
• Add support for IAsyncDisposable by @mgravell in https://github.com/protobuf-net/protobuf-net.Grpc/pull/272
• Improve service trace message by @pingvin13...

• fix race condition in cancellation cleanup (#144)
• fix ordering of descriptors in reflection respone (#143, #153)
• add support for custom metadata lookup in service-binder (#121, #138)

• try to improve blazor linker support (i.e. avoid removal of necessary APIs)

• support sub[SubService] (imports one interface inside another top-level service interface) (#206 via meirkr; also protobuf-net #859)
• automatically resolve Google.Protobuf IMessage types used in APIs

• update library references
• drop net461 (moving to net462 as lower bound); drop netcoreapp3.1 and net5.0 (moving to net6.0/netstandard2.1 as lower bound)
• improve handling of IDisposable and delegates in services (#199 by lanfeust69)