Document table-list alias for building a field list with select grid and separate question text

https://forum.getodk.org/t/xlsform-template-few-missing-appearances/43671/5?u=ln

Start by reading the linked forum discussion to understand the requested table-list alias and the select grid use case. Then locate the relevant Sphinx documentation in this repository; the work is done when the alias and its separate question-text behavior are clearly documented.

Written by the indexing model from the issue text.