ISourceControlProvider::TryToDownloadFileFromBackgroundThread

Executes the [FDownloadFile](API\Developer\SourceControl\FDownloadFile) operation, but unlike the [Execute](API\Developer\SourceControl\ISourceControlProvider\Execute\7) method this can be called from a background thread, this works because [FDownloadFile](API\Developer\SourceControl\FDownloadFile) is thread safe and it does not change the state of source control.