Wrong Down key handling around emojis

[palant]

Steps to reproduce:

1. Copy the text “test 😆” into the publish widget.
2. Press Left/Right keys to position the caret before the emoji but after the whitespace preceding it.
3. Press Down key.

This should result in the caret being positioned at the end of the text. That’s what happens when the caret is anywhere but before the emoji, and that’s what happens if the emoji is replaced by a letter.

Instead, the caret briefly goes to the end of the text only to jump back to the position before the emoji immediately.