completion: show doc in a tooltip instead of as a tree node
This has a few advantages:
- More usable out of the box, if the completion you select has doc, it will auto show up and will have more text visible than what we already have
- No expand buttons needed anymore which allows the completion item texts to use more space
- Since there are no expand buttons, things look more uniform and don't jump when items are filtered and the filtered items don't have any docs.
- Allows using setUniformRowHeights which is good for performance
- Allows dropping the KTextWidgets dependency (haven't done it yet)
See the video: