ibc/04-channel: import export GenesisState

[fedekunze]

Closes: #5948

Description

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

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For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #6087 into master will increase coverage by 0.20%.
The diff coverage is 91.15%.

@@            Coverage Diff             @@
##           master    #6087      +/-   ##
==========================================
+ Coverage   54.57%   54.78%   +0.20%     
==========================================
  Files         436      437       +1     
  Lines       26296    26436     +140     
==========================================
+ Hits        14352    14482     +130     
- Misses      10952    10958       +6     
- Partials      992      996       +4     

[cwgoes]

Not sure about the Channel changes.

[cwgoes]

utACK