Unlock utxos during dual funding failures

[t-bast]

When an alternative funding transaction confirms, we need to unlock other candidates: we may not have published them yet if for example we didn't receive remote signatures.

This is a breaking change in codecs since #2274, but shouldn't impact anyone if we merge this before people start using dual funding.

[t-bast]

The new trait is a bit verbose, but it highlights the fact that this is only used when the funding tx is unconfirmed (which wasn't obvious before). Alternatively, we could just use an Option[Either[Transaction, SignedSharedTransaction]], let me know what you prefer.

What is still a bit confusing is that in the single-funded case, this can be None for two very different reasons:

1. The funding tx is confirmed
2. The funding tx is unconfirmed but we're fundee so we don't have it

The dual-funded case doesn't have this ambiguity. I don't know if it's worth fixing for the single-funded case, it would mean wrapping another Option in the SingleFundedUnconfirmedFundingTx case class.

[codecov-commenter]

Codecov Report

Merging #2390 (764ec6d) into master (a97e88f) will decrease coverage by 0.05%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master    #2390      +/-   ##
==========================================
- Coverage   84.73%   84.68%   -0.06%     
==========================================
  Files         199      199              
  Lines       15458    15472      +14     
  Branches      642      640       -2     
==========================================
+ Hits        13098    13102       +4     
- Misses       2360     2370      +10     

Impacted Files	Coverage Δ
...inq/eclair/channel/fsm/ChannelOpenDualFunded.scala	91.55% <0.00%> (-0.41%)	⬇️
...in/scala/fr/acinq/eclair/channel/fsm/Channel.scala	84.51% <14.28%> (-0.41%)	⬇️
...in/scala/fr/acinq/eclair/channel/ChannelData.scala	98.11% <50.00%> (-1.89%)	⬇️
...acinq/eclair/channel/fsm/DualFundingHandlers.scala	60.46% <50.00%> (-1.70%)	⬇️
...ire/internal/channel/version3/ChannelCodecs3.scala	98.54% <75.00%> (+0.02%)	⬆️
...fr/acinq/eclair/channel/InteractiveTxBuilder.scala	86.21% <100.00%> (-0.51%)	⬇️
...la/fr/acinq/eclair/channel/fsm/ErrorHandlers.scala	81.13% <100.00%> (ø)
...ire/internal/channel/version0/ChannelCodecs0.scala	95.65% <100.00%> (ø)
...ire/internal/channel/version1/ChannelCodecs1.scala	96.96% <100.00%> (ø)
...ire/internal/channel/version2/ChannelCodecs2.scala	98.46% <100.00%> (ø)
... and 4 more