frontend: editor: Input Widgets are not configurable in Mini Widget Bar widgets

[ES-Alexander]

Bug description

Attempting to configure an Input Widget in a Mini Widget Bar widget results in the following error:

They work fine to configure in Custom Widget Base widgets, and the Bottom Bar, although per #1585 they can't even be added to the Top Bar.

Steps to reproduce

1. Open Edit Mode
2. Add a Mini Widgets Bar widget
3. Add an Input Widget to it
4. Try to configure it
5. It doesn't work, and gives an error message

Primary pain point(s)

Dragging them to a different place to be able to configure them is really clunky and unintuitive - they should be configurable wherever they are in the View.

Additional context

Possibly related to #1479.

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.

[rafaellehmkuhl]

I believe the best (and right) way to fix that is by making the Input widgets be regular MiniWidgets and untying the whole configuration logic from outside them.

Not the easiest way to fix, but will pay off in the long term.