Pass the BoundField instance to the Widget.render

[Christophe Henry]

Django 4's form rendering API is nice, but lacking a important feature to me: the Widget used to render a particular Field doesn't have any access to the corresponding BoundField. This makes rendering the field, label, potential error messages altogether as well as more more complex structures — like fields with subfields, for instance — impossible to render atomically within the widget. If you want to do that, you're forced to go up to the Form's template itself.

My opinion is that ​`Widget.render` should be passed the corresponding BoundField instance.

This would, I think, have 2 benefits:

1. allow easier rendering of complex widgets like ​ChoiceWidget using an iteration on the ​BoundField (​which is what's documented and would allow unification with ​ChoiceWidget.options and ChoiceWidget.optgroups)

2. allow rendering together Form fields that are related since BoundField has access to the parent Form (for instance a form with three options: email, phone, and other, respectively related to an email input, a phone input and a text input that are displayed below each).

P.S.: This is a feature request but I'm still opening a bug here since I can't join the django-developers mailing-list without a Google account.

[Mariusz Felisiak]

Duplicate of #33166 (see also #34077).