bug: Input widgets cannot be placed in the header bar

[ES-Alexander]

Bug description

Input widgets can be placed everywhere that normal mini-widgets can be (e.g. the bottom bar, mini-widget bars, and Custom Widget Bases), except for the header bar.

Steps to reproduce

1. Open edit mode
2. Try to drag an Input Widget to the header bar
3. It doesn't work

Primary pain point(s)

It's unintuitive to have one mini-widget space where only input-widgets can't go, and doesn't match the documented behaviour.

Additional context

No response

Prerequisites

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