Edits pkgdown + fixup of some docs

[olivroy]

Regression from #1694 caught by skimming through package index.

Also renamed the locations topic to include a link to main. Adding text_case_when() to the list of functions that use locations.

Somehow you can add links in @family tags! but pkgdown::has_concept() doesn't really recognize it (but that is okay, we can just revert to using starts_with("cells_"), like it was before #1658 Reverted this bit with gert::git_reset_hard("HEAD~2") ! (advice from r-lib/pkgdown#2647 (comment))

[rich-iannone]

This is great, thank you!