Press-and-Hold for Alternative characters

### Problem

The composer key used in Linux has a steep learning curve and involves a lot of memorising. In my experience, this system has reduced my productivity a lot coming from macOS.

### Proposal

Implement a way to type alternative characters by pressing-and-holding the keys on a keyboard.

### Prior Art (Optional)

KDE has recently introduced this future which you can read more about here:
https://blogs.kde.org/2026/03/14/this-week-in-plasma-press-and-hold-for-alternative-characters/

https://github.com/user-attachments/assets/44dd82f4-38d4-4276-95ea-d614694dbd2c

MacOS, iOS and Android have had for many years.