[Mobile] Wrong cursor position with arrow up/down

[aleripe]

I noticed a problem in the latest version (which is very good BTW!). If I have a long text and move up/down using the arrows everything works properly. Then if I tap on a different line the cursor goes to the expected position, but if I move up/down using the arrow it starts from the previous position and not from the updated one after I tapped. Left/right arrows works fine, instead.

Problem is easily reproduced running the repo example in the Android emulator:

1. Tap before "Rich text editor for Flutter"
2. Use the arrow down until "Track personal and group journals"
3. Tap again before "Rich text editor for Flutter"
4. Use the arrow down and you'll see cursor position is wrong
5. Tap again before "Rich text editor for Flutter"
6. Use the right arrow and you'll see cursor position is right

I've tried tracking down the issue in the code base but without luck... my understanding on how flutter_quill works is still limited.