Keyboard layout: Bigger font for test field

### Problem

Some languages have more complex diacritics. Having to test out between several finnish layouts, it was not always clear whether something was å, ä or á without having to change system font size

At a glance once set people do not look closely, but the input field to test layout is one of those times where people do

### Proposal

Increase the font size, maybe also spacing, for the test layout widget, since people will need to check for proper diacritics

### Prior Art (Optional)

_No response_