Make sure there is no attempt to re-attach DETACHING channel after connection becomes SUSPENDED

[lawrence-forooghian]

See internal conversation.

We think the spec does not define what should happen when the following sequence of events occurs:

1. the user calls detach(), putting the channel into DETACHING;
2. some time after, the connection becomes SUSPENDED;
3. some time after, the connection becomes CONNECTED again.

In particular, does the channel reattach and start receiving messages again? The desired behaviour is that it not do so. The way in which to make this happen is probably to make sure that the channel ends up in the DETACHED state when the connection becomes SUSPENDED.

The aims of this task are to:

• make sure that this behaviour is specified
• once specified, create SDK repo issues to implement this
• in particular, implement in JS as a priority

[sacOO7]

Yeah, I agree, if connection goes suspended and existing channel state is detaching, then it should go detached. This also goes as per https://sdk.ably.com/builds/ably/specification/main/features/#RTL5j
Mainly, Connection state change side effects spec needs a revision based on the given channel state.