Allow light/dark icon theme preference

[Amparose]

Currently an icon theme is set with "icon_theme": "Material Icon Theme",.

I would like it to work like themes:

"icon_theme": {
    "mode": "system",
    "light": "Zed (Default)",
    "dark": "Material Icon Theme"
  },

[drupol]

Looking for the same thing too.

[tkgalk]

How is this not a thing since theme support that already? Argh. This needs to be converted to an issue, I believe.

[Amparose]

I have nfi how that works. I guess someone important needs to see it?

Edit
Oh wait... might be my responsibility → #24695

[tkgalk]

I added an issue here already. #24638