[DX] hook_field_*_settings_form() should have $form and $form_state parameters

This is the respective issue as https://www.drupal.org/node/1391196

The hooks for instance and widget settings, hook_field_widget_settings_form() and hook_field_instance_settings_form() both return form arrays, but receive no information at all about the larger form they're inserting into.

This means that they can't add more complex behaviours such as dependencies and ajax -- hook_form_alter has to be used instead.

That ticket was switched from D8 to D7 which back in 2013, with this comment:

Field types are no plugins, so this doesn't apply anymore to D8. I'm not even sure whether we can change those function signatures in D7 though ... feels like a won't fix to me.

Well, thankfully we have no problem with API additions in Backdrop (so long as we are not breaking backwards compatibility)...

PR by @klonos: https://github.com/backdrop/backdrop/pull/2533