The intention here is to make things more testable going forward.
Specifically, to remove the "back-door" entrance into `BeatmapCarousel`
where `BeatmapSets` can be set by tests and bypas/block realm retrieval.
Closes https://github.com/ppy/osu/issues/31038.
If you don't realise why this does anything, realise this: the drawable
creation callback runs for every created sprite text in the text flow.
ANd the created sprite texts are split by whitespace. And Russian /
Ukrainian / Polish etc. use spaces as thousands separators.
So on those languages the first encountered part of the score would
duplicate itself to the remaining parts.
I'm actively convinced it was _more difficult_ to produce what was in
place in `master` than to do it properly. Why did `TextColumn` even have
`LocalisableString Text` and `Bindable<string> Current` next to each
other?????