Timing out packets on ordered channels when in flushing state

[damiannolan]

Originally came up in #4425.

Timing out packets on an ordered channel normally results in a channel state of CLOSED.

Aborting an upgrade if the upgrade timeout has passed results in an OPEN channel with an error receipt written AND upgrade state is removed.

What is the desired state of a channel end after a packet on an ordered channel times out when in flushing?

We could allow timing out packets when flushing on ordered channels, however if application logic is dependent on strict ordering then we may end up in bad/undesired states.

Adding needs discussion label

Originally posted by @damiannolan in #4425 (comment)

[damiannolan]

After discussion we've determined the desired end state here is likely:

• Packet is timed out successfully
• Channel upgrade is aborted and upgrade info deleted
• Channel is now in CLOSED state

cc. @AdityaSripal for visibility