* Misc cleanup
- Replace !List.isEmpty with List.isNotEmpty
- Remove redundant case in MoreScreenModel
- Drop no-op StateFlow.catch
- From lint warning:
> SharedFlow never completes, so this operator typically has not
> effect, it can only catch exceptions from 'onSubscribe' operator
* Convert DownloadQueue queue to MutableStateFlow
Replace delegation to a MutableList with an internal
MutableStateFlow<List>.
In order to avoid modifying every usage of the queue as a list, add
passthrough functions for the currently used list functions. This
should be later refactored, possibly by inlining DownloadQueue
into Downloader.
DownloadQueue.updates was a SharedFlow which updated every time a
change was made to the queue. This is now equivalent to the queue
StateFlow.
Simultaneous assignments to _state.value could cause concurrency
issues. To avoid this, always modify the queue using _state.update.
* Add Download.statusFlow/progressFlow
progressFlow is based on the DownloadQueueScreenModel implementation
rather than the DownloadQueue implementation.
* Reimplement DownloadQueue.statusFlow/progressFlow
Use StateFlow<List<T>>.flatMapLatest() and List<Flow<T>>.merge() to
replicate the effect of PublishSubject.
Use drop(1) to avoid re-emitting the state of each download each time
the merged flow is recreated.
* fixup! Reimplement DownloadQueue.statusFlow/progressFlow
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