[RFC] Finalize how onChange handles subsequent values

[Sawtaytoes]

In the original implementation at Minted, onChange did its thing only once and there was nothing about subsequent updates.

In OneForm, I added a handler for subsequent updates, but it hasn't been well-tested.

One of the things I want to do is reconfigure the onChange to have the same API as validations and groupValidations. I'm thinking that would make the idea of subsequent changes easier to manage.

As it stands today, I'm not sure exactly how to avoid infinite loops, but there are other reactive libraries that solve this problem.