[Feat]: Extend ComboboxOption to support disabled state of menu items

### Code of conduct

- [X] I agree to follow this project's code of conduct.

### Impacted component(s)

Combobox

### Description of the requested feature

As a user I'd like to disable certain items in a combobox so I can see that those values/items exists, but aren't selectable.

### Mockups or screenshots

### Implementation notes or ideas

Extend Combobox options with boolean param: `disabled` , see: https://github.com/adobe/spectrum-web-components/blob/a2b6bea7142930d8143d9ca887e2c56ffa71a669/packages/combobox/src/Combobox.ts#L45
such as
```
export type ComboboxOption = {
value: string;
itemText: string;
disabled: boolean;
};
```

and map that disabled state to related menu-item. Check if selection process will still work and disabled menu item won't be selected when user presses keyUp/keyDown.

Start in packages/combobox/src/Combobox.ts at the ComboboxOption definition, then trace how options are mapped to related menu items and how keyboard selection handles keyUp/keyDown. Done means options can carry a boolean disabled state, the menu item reflects it, and disabled items are not selected by keyboard or other selection paths.

Written by the indexing model from the issue text.