Missing focus disabled, hovered, focused and pressed icons on alot of control themes

[Shadowblitz16]

Describe the project you are working on

Windows95 theme

Describe the problem or limitation you are having in your project

Some styles are not possible do to the fact that some controls don't have icons and colors for some states

Describe the feature / enhancement and how it helps to overcome the problem or limitation

For example PopupMenu doesn't have any colors for icons as well as no pressed, focus or hovered icons for checkboxes and radio

Tree has same problems with all of it's icons

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Maybe a better bet would be to have a icon style resource instead of using raw images where you can have normal, focused, hovered, disabled, and pressed icons with a shadow like in #6576

If this enhancement will not be used often, can it be worked around with a few lines of script?

No

Is there a reason why this should be core and not an add-on in the asset library?

It improves theme customization of pixel art themes

[Calinou]

There's a PR to add a pressed style to PopupMenu's, but it needs to be redone from scratch given PopupMenu was refactored in 4.0: godotengine/godot#29268

[Shadowblitz16]

I was thinking maybe grouping font, font size, separation and spacing constants and styles under a single resource and then having that resource for all the states might be better.
That way when new controls are added the or theme styles it has to be implemented for all controls and control states