New Examples: Three select lists

We've had a couple of people ask for how to do three select lists, where the JSON in the first populates the other two.
- Start with a single select.
- When a value is chosen for select 1, show select 2 and populate it from the first choice
- When a value is chosen for select 2, show select 3 and populate it from the second choice
- There should be no errors in the console

Trickier: do another one (same example or separate), but in a datagrid. Use the instance.rowIndex to figure out what the "parent" select is.

Start by locating the existing single-select example and the related datagrid example or entry point. Add a chained three-select example where each choice reveals and populates the next list, then verify the datagrid variant uses the appropriate row relationship and produces no console errors.

Written by the indexing model from the issue text.