Add Combo-box widget

[axieum]

Describe the solution you'd like
The addition of a new Combo box widget.

Additionally, I would like a way to customise the dropdown components, e.g. to add an icon next to each item.

Additional context
Windows Run dialog -

Combo box example -

Autocomplete example -

[tmudway]

I looked into this somewhat and the core issue preventing easy implementation is how the onClick triggers are hooked up.

The instant that a combobox dropdown exits the bounds of its parent panel, it no longer registers mouse input. The workaround I'm using for this is to just forgo mouse input and instead use up/down arrow keys to select an option, with the list filtering based on the contents of the central WTextField widget. This ends up sorta like how autofill works in the vanilla minecraft chatbox