bug(linux): Backspace doesn't work properly with text selection

Install and activate Khmer Angkor or IPA (SIL) keyboard.

## Scenario 1

### To reproduce
- open gedit
- type a few characters
- select the last three characters selecting from right to left, i.e. starting at the end
- press backspace

### Expected behavior:
- selection gets deleted

### Actual behavior
- character before the selection gets deleted, selection remains selected

## Scenario 2

### To reproduce
- open gedit
- type a few characters
- select the last three characters selecting from left to right.
- press backspace

### Expected behavior
- selection gets deleted

### Actual behavior
- last character gets deleted, selection consists now of two characters. To delete the entire selection, the user has to press backspace three times.

## Environment

Tested on Ubuntu 22.04 and 23.04 with X11 and Wayland. Keyman 17 alpha.