* Rename functions for DownloadService internal use
* Call DownloadService.start via DownloadManager
* Inline DownloadService.stop into pauseDownloads
* Inline DownloadService.stop into clearQueue
NotificationReceiver will now also stop the DownloadService when
receiving ACTION_CLEAR_DOWNLOADS.
* Provide DownloadService.isRunning via DownloadManager
1:1 translation from the RxJava implementation, should match the
previous behavior.
Dropped the return value from functions of the form
```
fun foo(t: T, ...): Observable<T>
```
where the Observable produced the original argument `t`.
The caller already has the result if necessary.
While this conversion is not flow-based overall, some sections use
flows to use the flatMapMerge and retryWhen operators.
Removed RetryWithDelay as it was only used here.
Inlined fetchAllImageUrlsFromPageList instead of converting it to a
suspending equivalent. fetchAllImageUrlsFromPageList is no longer
used in the app, but was not removed as it is part of source-api.
(However, it does not seem to be used exposed in extensions-lib or
used in tachiyomi-extensions.)
runBlocking is used as a temporary stop-gap.
When restarting a download, the page count would display as 0 until
the first page download completion, after all the existing pages were
rechecked.
To fix, calculate downloadedImages from pages instead of relying on
the downloader to reset and increment the count.
Includes side effects:
- No longer need to restart app for user agent string change to take effect
- parseAs extension function requires a Json instance in the calling context, which doesn't necessarily need to be the default one provided by Injekt
`it.id` is the source ID of the source being sorted.
`state.value.manga!!.id` is the manga ID of the selected manga.
`state.value.manga!!.source` is the source ID of the selected manga.
(cherry picked from commit dc2eaf0788)
