That PR wasn’t tested nor reviewed adequately.

That PR wasn’t tested nor reviewed adecuately.

For GRPCOperation's, ensure finish _handler can only be called once, and release it when called, so weak ptrs needn't be used with it, and the call won't be released until the finish handler is called.
When the connectivityMonitor determines the connection has been lost, pull the host disconnect call. Creates an unreliable connection when connectivity is restored. Calling finishWithError: is sufficient.

Move C-layer call creation into GRPCChannel, so that it always acts on a
non-destroyed channel.

Listen for connectivity in the GRPCCall, and destroy the channel.

TODO:
- Documentation
- Make public
- Check I’ve implemented all NSMutDict required methods

So we can make the property a dictionary later, by just extending
NSMutableDictionary to conform to the protocol.

Also clarify in GRXWriter.h that the writeable is released whenever the
writer finishes.

And move it to the RxLibrary.

Fixes https://github.com/grpc/grpc/issues/2194 .