In timeout processing, account for moving channel state to flush complete

[colin-axner]

Summary

Requires:

• Store counterparty upgrade in ack handler #4260
• Add store funcs for counterparty upgrade timeout #4233

Add the following spec changes to TimeoutExecuted function in 04-channel.

    if channel.state == FLUSHING {
      upgradeTimeout = privateStore.get(counterpartyUpgradeTimeout(portIdentifier, channelIdentifier))
      if upgradeTimeout != nil {
        // counterparty-specified timeout must not have exceeded
        // if it has, then restore the channel and abort upgrade handshake
        if (upgradeTimeout.timeoutHeight != 0 && currentHeight() >= upgradeTimeout.timeoutHeight) ||
            (upgradeTimeout.timeoutTimestamp != 0 && currentTimestamp() >= upgradeTimeout.timeoutTimestamp ) {
                restoreChannel(portIdentifier, channelIdentifier)
        } else if pendingInflightPackets(portIdentifier, channelIdentifier) == nil {
          // if this was the last in-flight packet, then move channel state to FLUSHCOMPLETE
          channel.state = FLUSHCOMPLETE
          publicStore.set(channelPath(portIdentifier, channelIdentifier), channel)
        }
      }
    }

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