Merge pull request #3961 from jcanizales/cocoadocs-format

src/objective-c/GRPCClient/GRPCCall+OAuth2.h

src/objective-c/GRPCClient/GRPCCall+Tests.h

src/objective-c/GRPCClient/GRPCCall.h

src/objective-c/GRPCClient/private/GRPCChannel.h

src/objective-c/GRPCClient/private/GRPCCompletionQueue.h

src/objective-c/GRPCClient/private/GRPCHost.h

src/objective-c/GRPCClient/private/GRPCSecureChannel.h

src/objective-c/GRPCClient/private/GRPCWrappedCall.h

src/objective-c/GRPCClient/private/NSError+GRPC.h

src/objective-c/ProtoRPC/ProtoMethod.h

src/objective-c/RxLibrary/GRXBufferedPipe.h

src/objective-c/RxLibrary/GRXConcurrentWriteable.h

src/objective-c/RxLibrary/GRXForwardingWriter.h

src/objective-c/RxLibrary/GRXImmediateWriter.h

src/objective-c/RxLibrary/GRXWriteable.h

src/objective-c/RxLibrary/GRXWriter+Immediate.h

src/objective-c/RxLibrary/GRXWriter+Transformations.h

src/objective-c/RxLibrary/GRXWriter.h

src/objective-c/RxLibrary/NSEnumerator+GRXUtil.h

src/objective-c/RxLibrary/private/GRXNSBlockEnumerator.h