feat(mac): support mnemonic keyboard

### Is your feature request related to a problem? Please describe.

Originally from https://community.software.sil.org/t/galaxie-hebrew-mnemonic-on-screen-keyboard-font-not-working/10871.

> I am using Keyman version 18.0.243 on an Australian Apple M3 Pro running Sequoia 15.6.1. The Galaxie Hebrew (Mnemonic) on-screen keyboard is not showing the font. Instead each key has a square box with a question mark in it.
>
> When I type, the Hebrew letters appear in applications … so it seems to be just an issue with the on-screen keyboard display.
>
> I have tried a different hebrew keyman keyboard and that works. So … any thoughts?
>
>

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Related issues

https://github.com/keymanapp/keyman/issues/3345#issuecomment-657744336

### Keyman apps

- [ ] Keyman for Android
- [ ] Keyman for iPhone and iPad
- [ ] Keyman for Linux
- [x] Keyman for macOS
- [ ] Keyman for Windows
- [ ] Keyman Developer
- [ ] KeymanWeb
- [ ] Other - give details at bottom of form

### Keyman version

_No response_

### Operating system

macOS

### Device

_No response_

### Target application

_No response_

### Browser

_No response_

### Keyboard name

galaxie_hebrew_mnemonic (+ mnemonic keyboards)

### Keyboard version

3.3.1

### Language name

he

### Additional context

_No response_