Add `incremental=true` to valid `parameters` key/value pair for geotrace and geoshape

In the XForms output, it should be a body attribute for the corresponding form control.

It should be optional. If any value other than `true` is provided, the attribute should not be included in the XForms output.

Spec discussion: https://forum.getodk.org/t/odk-xforms-spec-proposal-add-incremental-true-attribute-for-geotrace-and-geoshape/57181