Error messaging: prompt for feedback

As part of a broader overhaul around errors (categorization/modeling, reference in types e.g. as a `Result` type, documentation of potential errors associated with a particular flow, etc), we should think about ways to associate a specific error condition with a prompt for user feedback about that error.

Background detail

I'm opening this as a stub issue and can flesh it out further if it's unclear. It comes up now in the context of rolling back some overly ambitious changes in #273, introducing support for non-string selects.

That functionality exceeds the current XForms spec. We originally decided to merge it anyway, but reconsidered after realizing it could cause problems downstream (e.g. conflicts between multiple typed `` values and database schemas derived from ``). We have decided for now to roll back that behavior, and to produce an error for forms which define a non-string bind type for:

- ``
- ``
- (Pending) ``

Discussing that decision, we talked about having the error messaging prompt for feedback, so we can get a better sense of user intent if the error does occur. My initial change will include language to welcome feedback, but stops short of including a link to provide feedback. I believe there should be more design around how we model something like that, and it intersects with other pending work around how we produce errors throughout the Web Forms project. I'm filing the issue now so I can link back to it in JSDoc for the corresponding stub error type.

(TODO: should we maybe try GitHub's "sub-issues" feature to organize issues on the broader topic of errors?)

Start by reviewing issue #273 and the corresponding stub error type referenced in JSDoc. Clarify how error conditions should be associated with feedback prompts across the broader error overhaul, including the non-string bind-type errors for select controls. Done means the design and scope are agreed rather than remaining a stub.

Written by the indexing model from the issue text.