New workspace icon rules should be able to be created for arbitrary workspace titles

### Feature Description

In settings, you can add icons if a workspace title matches some name. At present, you can only see/edit/add these for each named workspace that actually exists on your computer at that moment.

It would be nice to be able to see all the rules whether or not the workspace is visible and add new rules for arbitrary titles right there in the settings menu

### Use Case

QOL improvement for dealing with named workspaces in DMS, and reduces invisible DMS state/configuration

### Compositor(s)

- [x] All compositors
- [ ] Niri
- [ ] Hyprland
- [ ] MangoWC (dwl)
- [ ] Sway
- [ ] Other (specify below)

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

Start at the settings menu's workspace icon rules, then trace how rules are currently limited to visible workspaces and how they are stored. Done means existing rules remain visible and editable, while a new rule can be created for an arbitrary workspace title; the issue names no files or tests to run.

Written by the indexing model from the issue text.