All other similar UI components have required dependencies, so this is
mainly to bring things in line with expectations. I am using this fact
in the skin editor to only show components which can be used in the
current editor context (by `try-catch`ing their
`Activator.CreateInstance`).
After the recent changes introducing cancellation support to
`WorkingBeatmap`, it turned out that if the cancellation support was
used, `GetPlayableBeatmap()` would raise timeout exceptions rather than
the expected `OperationCanceledException`.
To that end, split off a separate overload for the typical usage, that
catches `OperationCanceledException` and converts them to beatmap load
timeout exceptions, and use normal `OperationCanceledException`s in the
overload that requires a cancellation token to work.
Apparently I wrote the BDL system and don't know how this works. I
believe you need `CancellationToken?` or CanBeNull=true, however that doesn't actually
play well when actually using the token in code...