Use trusted block next validators when building header

[ancazamfir]

Closes: #770

Description

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For contributor use:

• Updated the Unreleased section of CHANGELOG.md with the issue.
• If applicable: Unit tests written, added test to CI.
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Updated relevant documentation (docs/) and code comments.
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[codecov-io]

Codecov Report

Merging #771 (9d80ce4) into master (b1b37f5) will increase coverage by 30.9%.
The diff coverage is n/a.

❗ Current head 9d80ce4 differs from pull request most recent head 587f4dc. Consider uploading reports for the commit 587f4dc to get more accurate results

@@            Coverage Diff            @@
##           master    #771      +/-   ##
=========================================
+ Coverage    13.6%   44.5%   +30.9%     
=========================================
  Files          69     166      +97     
  Lines        3752   11386    +7634     
  Branches     1374       0    -1374     
=========================================
+ Hits          513    5078    +4565     
- Misses       2618    6308    +3690     
+ Partials      621       0     -621     

Impacted Files	Coverage Δ
...application/ics20_fungible_token_transfer/error.rs	0.0% <ø> (ø)
...ion/ics20_fungible_token_transfer/msgs/transfer.rs	22.2% <ø> (ø)
..._transfer/relay_application_logic/send_transfer.rs	85.7% <ø> (ø)
modules/src/events.rs	0.0% <ø> (ø)
modules/src/handler.rs	100.0% <ø> (ø)
modules/src/ics02_client/client_consensus.rs	55.8% <ø> (ø)
modules/src/ics02_client/client_def.rs	32.3% <ø> (ø)
modules/src/ics02_client/client_state.rs	65.1% <ø> (ø)
modules/src/ics02_client/client_type.rs	79.1% <ø> (+31.5%)	⬆️
modules/src/ics02_client/context.rs	90.4% <ø> (ø)
... and 266 more

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[ancazamfir]

The first solution/ commit does not work as the next_validators() in the LightBlock doesn't have the proposer set and on-chain validation fails the update because of this. So I changed to pull the header at trusted_height + 1 and pass the trusted_height in build_header(). Also had a version that decrements the trusted_header.height() inside build_header(). I thought that look just a bit uglier. Can't think of a better solution until we refactor the light client.

[adizere]

LGTM