Add support for multiple connection hops in tx chan-open-ack

[joaotav]

Part of: #3940

Summary

tx chan-open-ack

• Replace call to tx_chan_cmd! macro with an inline function on TxChanOpenAckCmd
• Add build_multihop_chan_open_ack() to method build_chan_open_ack_and_send() to enable the construction of MsgChannelOpenAck messages when multiple connection hops have been specified.
• Modify validated_expected_channel() to support channel ends with multiple connection hops on the destination chain.

Tests

• Manual testing for single-hop channel handshake
• Manual testing for multihop channel handshake with 2 connection hops
• Manual testing for multihop channel handshake with 2+ connection hops

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[romac]

Done in #4050