Add `unsafe_funding_transaction_generated`

[jbesraa]

..under ChannelManager. It replicates the functionality of the original funding_transaction_generated in the same module but without checking if the witness data is set in the funding transction inputs.

#3022

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.87500% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 89.83%. Comparing base (38690bf) to head (2e18e65).

Files	Patch %	Lines
lightning/src/ln/functional_test_utils.rs	96.55%	1 Missing :warning:
lightning/src/ln/functional_tests.rs	95.45%	1 Missing :warning:

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3056      +/-   ##
==========================================
- Coverage   89.84%   89.83%   -0.01%     
==========================================
  Files         116      116              
  Lines       96303    96367      +64     
  Branches    96303    96367      +64     
==========================================
+ Hits        86521    86573      +52     
- Misses       7225     7232       +7     
- Partials     2557     2562       +5     

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[jbesraa]

@TheBlueMatt while working on this I noticed the funding_transaction_generated would actually work with an empty array of inputs in the funding transaction.. is that by design?

[jbesraa]

closing as this will be covered in #3024