FIx the fix of Issue 1656

[kbrevoort]

Summary

This PR makes a series of technical corrections to pull request #1716 to resolve issues that were pointed out by @nielsbock and @bzkrouse. It also contains a few other minor improvements to the code to make it more robust. There's no new functionality, just minor tweaks to make the functionality added to address #1656 more reliable.

Related GitHub Issues and PRs

• Ref: Column spanners do not comply with widths set by cols_widths() for latex tables #1656
• Ref: Fix Issue1656 #1716

Checklist

• I understand and agree to the Code of Conduct.
• I have listed any major changes in the NEWS.
• I have added testthat unit tests to tests/testthat for any new functionality.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[rich-iannone]

This is really great, thank you!!

[rich-iannone]

LGTM!