Arrow keys should move selection to cell next/previous/above/below cell

[pjasiun]

Generalised issue

Arrow keys work differently in all browsers and in all of them they don't do what the user would expect:

• Chrome moves the selection to the right cell if you press down arrow.
• In Firefox arrow keys don't do anything useful.

We need a custom handler for arrow keys. However, it's a non-trivial task due to issues described in https://github.com/ckeditor/ckeditor5-table/issues/108#issuecomment-465529187. We will need to, at least partially, use the browser native handling and try to do something with that.

Original issues

I wanted to fill the table column and I was surprised that when I press down key selection moved to the cell on the right, not below. The same for arrow up - selection should be moved to the cell above, not on the left. The current behavior makes filling column very inconvenient.

[jodator]

I AFAICS we left it to the browsers. But also for me the expected behavior is such that using arrows would allow to navigate up/down visually as it does on Chrome.

ps.: it works as described in Firefox

[Reinmar]

Yep, for now we do nothing and let the browser decide. We can change it at any time.

[Reinmar]

Just so you know – this is a tricky issue. Pressing down arrow in a cell might move the selection to another line of text in the same cell or may need to move it to another cell. We may look for some hacks though, like handling the arrow keys only if the selection is at the very beginning/end of a cell. That'd handle empty cells as wells as non-empty ones but with an additional step of first moving your caret to the very end of the content and then moving to the next cell.

[Reinmar]

Another case: https://github.com/ckeditor/ckeditor5-table/issues/175

[jodator]

Closing as already implemented and a dup of #3267.