JIRA: https://jira.spring.io/browse/INT-4351
The `WatchService` reacts to the events in the file system and keep
track ove the events until we poll them, e.g. via `listEligibleFiles()`
in the `WatchServiceDirectoryScanner`.
On the other hand the `SourcePollingChannelAdapter` calls the mentioned
`listEligibleFiles()` according its polling period.
At this moment the `FileListFilter` is applied to the polled files.
It may happen that `LastModifiedFileListFilter` can't accept too young
files yet and they are lost for the future consideration.
* To allow, for example, to retain young files by the
`LastModifiedFileListFilter` judgment for the future cycles add
`DiscardAwareFileListFilter` with the `DiscardCallback` support.
The `WatchServiceDirectoryScanner` now registers such a callback into
the filter and stores discarded files into the `filesToPoll` queue
for the future poll cycle.
**Cherry-pick to 5.0**
Fix compilation warnings
* Replace `DiscardCallback` with the plain `Consumer`
* Ensure uniqueness in the `WatchServiceDirectoryScanner` internal
queue via a `Set` implementation, since discard callback may be called
several times for the same file from the `CompositeFileListFilter`
according to its nature
* Add JavaDocs and Docs
Change `@since` to `5.0.5`
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