Realizing that, with the keyword argument spread syntax, I don't need
to do merging, I can just. spread at the right place!
My rationale for the ordering here is: if the caller theoretically tried
to override the builder (even though I don't see why), I think we would
want to respect that. Whereas the `class` argument should be overridden
because we're safely *merging* our `.support-form` class into it.
I want to reuse this for unlabeled pet styles is why! (That's been the
immediate motivation for this refactor, but also I do just like that
it'll make support forms easier to build.)
I think helpers are fine for the simpler ones that are basically *just*
wrapper tags, but once it starts getting into `concat`, I think that's
too unfamiliar of a syntax for developers; let's bail into our usual
templating system!
I'm not sure about putting them in `application/support_form` like this.
That's cute for one-offs like `application/hanger_spinner`, because
`render partial: "hanger_spinner"` assumes the `application` view folder
by default, but that doesn't work once it's nested: it looks for a
`views/support_form` folder.
I think maybe it could soon be time to bail from the strict "view
folders belong to controllers" thing, similar to how we did for
`SupportFormHelper`, and add a `components` folder or similar? Idk, not
sure yet!
Instead of hand-rolling HTML, this offers helpers like `f.field`, to
help ensure the HTML is consistent, and to keep the templates more
focused on the unique form elements.
