[DONOTMERGE] chore: add 668 functions to tendermint client

[notbdu]

Description

Adds #668 functions to the tendermint client and refactors CheckHeaderAndUpdateState() to use the the added functions internally. This ensures we're covering the same code in tests.

closes: #879

NOTE: This PR depends on #898 to be merged first as this is branched off header changes there.

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• 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
• Review Codecov Report in the comment section below once CI passes

[colin-axner]

thanks for this work! We have altered the code a bit from the original proposal in the linked issue so now these changes are outdated. Closing. Thanks again!