Add channel funding txo to Channel Event::ChannelClosed

[optout21]

Reworked on top of #2809

Fixes #2772

• extend ChannelClosed event with optional original channel funding txo; to help checking for the existence and confirmation status of the closing tx
• internally extend ShutdownResult with funding txo
• add checks for the new field of the event, in 2 test cases
• also add checks for field user_channel_id (just for completeness)

[shaavan]

The changes look good, and I think this PR can benefit by extending the test suite to cover this new change.

A few suggested nits I believe can further improve this PR.

[optout21]

Minor changes from review. Changed internal from_finish_shutdown to take a sinlge ChannelContext instead of capacity, user ID and txo fields.
TODO: Add checks for the contents of the new event field; squash.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (7bc2a14) 88.79% compared to head (efaba11) 89.19%.
Report is 43 commits behind head on main.

Files	Patch %	Lines
lightning/src/events/mod.rs	80.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2800      +/-   ##
==========================================
+ Coverage   88.79%   89.19%   +0.39%     
==========================================
  Files         114      114              
  Lines       95767    98266    +2499     
  Branches    95767    98266    +2499     
==========================================
+ Hits        85038    87649    +2611     
+ Misses       8289     8151     -138     
- Partials     2440     2466      +26     

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[shaavan]

LGTM!

• The suggestions mentioned above are addressed.
• The test suite is extended appropriately to address the current changes, and the tests work perfectly.

[vladimirfomene]

ACK 11fe6ae. LGTM

[TheBlueMatt]

Ugh, this basically LGTM, but in #2809 I rewrote the shutdown logic to move the event generation to clean up some of this logic. Is there any chance you want to rebase on that? Otherwise I'll merge this and have to partially revert it to rebase #2809 on top.

[optout21]

Ugh, this basically LGTM, but in #2809 I rewrote the shutdown logic to move the event generation to clean up some of this logic. Is there any chance you want to rebase on that? Otherwise I'll merge this and have to partially revert it to rebase #2809 on top.

I'll redo this on top of #2809

[TheBlueMatt]

Thank you!

[optout21]

This is now reworked on top of #2809 . Became simpler. Keeping as Draft until #2809 is merged.

[TheBlueMatt]

Nice, thanks.