feat(web): an option to adjust font size on touch keyboards

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

From the community site (https://community.software.sil.org/t/feature-request-an-option-to-adjust-font-size-on-touch-keyboards/10477)

> Since some fonts are bigger and occupy more space than other fonts of the same size, then depending on the
> keyboard font, the hint character may jam with the main character(s) on a key. What if there is an option for keyboard authors to adjust font size, either by setting numerical values or by zooming in or out by percentage?
>
> Example:
> Attached is a screenshot comparing a Keyman Keyboard with Gboard (the Google keyboard). Note how the keys SH and H and their hint characters jam.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Related issues

_No response_

### Keyman apps

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

### Keyman version

_No response_

### Operating system

_No response_

### Device

_No response_

### Target application

_No response_

### Browser

_No response_

### Keyboard name

_No response_

### Keyboard version

_No response_

### Language name

_No response_

### Additional context

_No response_