feat(developer): Hotkey/rapid swap between default and shift views when editing a mobile keyboard

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

Some .kmn files have characters grouped by the character type, rather than separated into distinct uppercase and lowercase groups. When manually converting a physical keyboard layout into a mobile layout, it can be tedious switching between the default and shift layouts to add each character one by one, especially on smaller screens where you must first scroll to access the dropdowns and keycap values respectively.
I like to have the .kmn code splitscreened with the touch layout editor so I can easily copy/paste the unicode between them, but this makes switching between layers quite slow.

### Describe the solution you'd like

Having a hotkey combination to toggle between the different Touch Layout layers would be handy, or on the more complex side, the ability to define rules for the layers in a single view (i.e. setting up upper and lower case characters at the same time).

### Describe alternatives you've considered

The current best alternative is to have Keyman at full width (still has a slight scrollbar, but all elements are at least partially on screen) and alt-tab between windows, or to have two monitors (unfortunately not an option at the moment).

### Related issues

_No response_

### Keyman apps

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

### Keyman version

17.0.326

### Operating system

Windows 10

### Device

Oryx Pro (System76)

### Target application

_No response_

### Browser

_No response_

### Keyboard name

_No response_

### Keyboard version

_No response_

### Language name

_No response_

### Additional context

_No response_