Search is not discoverable in Focus Mode

### Expected

In Focus Mode, when using the search function, users can see what they are typing.

### Observed

When Focus Mode is active, using the search has the user typing on a search box that's invisible to them.

It takes a few times to realize that the search box is hidden and is only shown when disabling Focus Mode, which is a confusing UX pattern.

### Reproduced

1. Start the app
2. Enable Focus Mode: `View` > `Focus Mode`
3. Go to `Edit` > `Search Notes`
4. Nothing happens in the UI. At this point the user will most probably think that the search is not working
5. Start typing.
6. If there are any matching keywords in the currently viewed note, they will be highlighted
7. Disable Focus Mode: `View` > `Focus Mode`
8. Realize that you had been typing invisibly is actually in the (now revealed) search box at the top of the`All Notes` sidebar

### Where did you see the bug

- System Make: N/A
- System Model: N/A
- OS: Ubuntu
- OS version: 20.04
- Browser (if applicable): N/A (app)
- Browser version (if applicable): N/A (app)
- Simplenote app version: 2.7.1

Reproduce the issue through View > Focus Mode and Edit > Search Notes, then trace the Focus Mode and All Notes sidebar search entry points. Done means activating Search Notes in Focus Mode visibly shows the search box and makes typed text discoverable without disabling Focus Mode.

Written by the indexing model from the issue text.