Move docs for locations helper into own topic

[olivroy]

Summary

This PR tweaks the docs for the cells_*() functions.

The idea is that there was duplication.

• This adds cross-refs between the functions that use locations (tab_style(), tab_footnote() and the text transforming text_*() functions.

This removes the description of other cells_*() in each cells*() topic and moves this to a central location. ?location-helper

This adds a couple of cross-refs to the location-helper topic to make it easy to preview it easily from the help pane.

The reason behind is that you usually don't really want to move between cells_* functions, but rather tab_* <-> cells_*().

For fixing _pkgdown.yml, I use has_concept() (topic matching)

Let me know if you like the approach or if you have suggestions on how to further improve it! I tried separating the commits as much as possible!

I am also able to use @InheritParams for locations and .locations as roxygen2 understands this pattern.

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.

[rich-iannone]

I really like this a lot! And it addresses something I was never really satisfied with (the really excessive repetition across so many docs). I’m thinking we go with this and make additional tweaks as necessary.

[rich-iannone]

Let me know when your changes are finalized. At that point I’ll review and merge.

[olivroy]

Yes! this is ready for review! I was done with my proposed changes

[rich-iannone]

LGTM!