Allow two-way integration for picklist fields in Azure DevOps when using the XML process model

This idea is a variation on https://big.ideas.aha.io/ideas/AFME-I-2, but the general use case is the same. I've been asked by Aha support to make a separate idea specifically for those using the XML process model, since this has supposedly been fixed for the inherited process model but it still does not work for those of us on the XML process model. As Microsoft has not provided a migration path, it is not feasible for us to upgrade to the inherited process model anytime soon.

From what I understand, the root of the issue is described here https://docs.microsoft.com/en-us/azure/devops/boards/work-items/work-item-fields?view=azure-devops "The isPicklist and isPicklistSuggested attributes are only assigned to custom fields defined for an inherited process."