feat(mobile): add bulk download functionality (#18878)

* feat(mobile): add bulk download functionality and update UI messages

- Added `downloadAll` method to `IDownloadRepository` and its implementation in `DownloadRepository` to handle multiple asset downloads.
- Implemented `downloadAllAsset` in `DownloadStateNotifier` to trigger bulk downloads.
- Updated `DownloadService` to create download tasks for all selected assets.
- Enhanced UI with new download success and failure messages in `en.json`.
- Added download button to `ControlBottomAppBar` and integrated download functionality in `MultiselectGrid`.

* translations use i18n method t()

* Update mobile/lib/services/download.service.dart

Co-authored-by: shenlong <139912620+shenlong-tanwen@users.noreply.github.com>

* fix(mobile): update download logic in DownloadService

- Changed the download method to utilize downloadAll for handling multiple tasks.
- Simplified remoteId check by removing unnecessary condition.

* sort i18n keys

* remove the download signature from interface and logic as we use the downloadAll now

---------

Co-authored-by: shenlong <139912620+shenlong-tanwen@users.noreply.github.com>

mobile/lib/providers/asset_viewer/download.provider.dart

@@ -140,6 +140,10 @@ class DownloadStateNotifier extends StateNotifier<DownloadState> {
     });
   }
 
+  Future<List<bool>> downloadAllAsset(List<Asset> assets) async {
+    return await _downloadService.downloadAll(assets);
+  }
+
   void downloadAsset(Asset asset, BuildContext context) async {
     await _downloadService.download(asset);
   }