struct IncomingEventsHandleStorage

|IncomingEventsHandleStorage| allocates the necessary storage for receiving

the handles for any one of the possible events defined in |FidlProtocol| from

its corresponding transport. It is useful for allocating bespoke amount of

memory when the code path is certain what is the protocol type, such as

during synchronous event handling.

|FidlProtocol| must be a protocol marker type.

This class is shared between wire and natural types - both receive messages

of the same shapes and then perform their own decoding.