Different themes and icons for light and dark modes

### Feature Description

Just what it says in the title. It would be nice to be able to set different themes for light and dark modes, same as wallpapers. Same thing for icon themes, since DMS doesn't (yet?) support recolorable icons, although I know a shell restart is required to update the icons. Maybe there's a fix for that, too?

### Use Case

_No response_

### Compositor(s)

All compositors

### If Other, please specify

_No response_

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_