Add a shortcut action for switching to a specific color scheme


Pretty self-explanatory.
```json
{ "action": { "command": "setColorScheme", "name": "<scheme name>"}, "keys": [] }
```

```c#

    [default_interface] runtimeclass SetColorSchemeArgs : IActionArgs
    {
        string Name { get; };
    };
```


I want this for the command palette, see #5400