Suggestion: add cross reference to styling geospatial data in Form Styling

It would perhaps be helpful to add a section in 'Form Styling' that has a summary of the fact you can manage the colour of points and lines plus the marker symbol and include a link back to the choice-properties section?

I would suggest Geospatial Data as the heading (for consistency) e.g. https://docs.getodk.org/form-styling/#geospatialdata

**REASON**: I was trying to remind myself of different ways of styling data on maps in the Docs and went to Form Styling... Then I used a search 'marker-color' and the results gave me https://docs.getodk.org/form-question-types/ So I had to find in the page and found it:

https://docs.getodk.org/form-question-types/#choice-properties

So that's logical, in that I am using it in a select question, but I was coming at it from a styling perspective (perhaps illogical) so looked there...

Oh, and github doesn't let me use SeeWhy :-)

Open the Form Styling documentation and compare its coverage with the choice-properties section in Form Question Types. Add the requested Geospatial Data cross-reference and summary, then verify that the Sphinx documentation build renders the section and link correctly.

Written by the indexing model from the issue text.