Add `required` attribute to MultiValueFields

fields.py

    def __init__(self, fields, *, require_all_fields=True, **kwargs):
        self.require_all_fields = require_all_fields
        super().__init__(**kwargs)
        
        # We have two sets of widgets. Each field in fields has a widget whilst self.widget is probably our `MultiWidget`
        # We're interested in the MultiWidget as this is what is rendered.
        # Let's loop over fields and the MultiWidget and set required on the subwidgets.
        for field, widget in zip(fields, self.widget.widgets):
            field.error_messages.setdefault('incomplete',
                                            self.error_messages['incomplete'])
            if self.disabled:
                field.disabled = True
                
            # still to agree actual logic for the following section.
            
            if (self.required and (self.require_all_fields or field.required)) or (
                not self.required and not self.require_all_fields and field.required
            ):
                field.required = widget.is_required = True
            else:
                field.required = widget.is_required = False
        self.fields = fields

widgets.py

    def get_context(self, name, value, attrs):
        context = super().get_context(name, value, attrs)
        if self.is_localized:
            for widget in self.widgets:
                widget.is_localized = self.is_localized
        # value is a list of values, each corresponding to a widget
        # in self.widgets.
        if not isinstance(value, list):
            value = self.decompress(value)

        final_attrs = context['widget']['attrs']
        input_type = final_attrs.pop('type', None)
        id_ = final_attrs.get('id')
        subwidgets = []
        for i, (widget_name, widget) in enumerate(zip(self.widgets_names, self.widgets)):
            if input_type is not None:
                widget.input_type = input_type
            widget_name = name + widget_name
            try:
                widget_value = value[i]
            except IndexError:
                widget_value = None

            if id_:
                widget_attrs = final_attrs.copy()
                widget_attrs['id'] = '%s_%s' % (id_, i)
            else:
                widget_attrs = final_attrs

            # Now that each subwidget has is_required set properly, lets add the attribute to the context here
            if widget.is_required and not widget.is_hidden:
                widget_attrs['required'] = True

            subwidgets.append(widget.get_context(widget_name, widget_value, widget_attrs)['widget'])
        context['widget']['subwidgets'] = subwidgets
        return context