Add virtual scrolling

[egbertbouman]

Fixes #8365.
Fixes #8492 by removing the need for pagination.

This PR adds virtual scrolling to all tables, including file trees. For lists of a couple of thousand items, the difference is quite dramatic. Before you could barely scroll, now there's no slowdown at all. I've tested with up to 100k items without any issues. I think/hope it's good enough to disable pagination.

A downside is that column sizes can change as you scroll through the list. That's just because the table layout is set to auto, and only a small set of rows is being rendered at a time. I didn't want to go into calculating column sizes manually, but we can always revisit this later.

Note that there is room for additional performance improvements by only requesting updates from the core for the items that are (close to being) visible. Maybe something to consider in the future.

[egbertbouman]

validate

[qstokkink]

Nice 👍 This fully obsoletes the TorrentFileTree now then, I think.

[egbertbouman]

Thanks! I wasn't brave enough to remove TorrentFileTree, as some people may prefer it.
It's also the normal way of displaying files (I think that e.g., QBittorrent uses trees too).