refactor(mobile): stack only through merging from timeline (#4598)

* mobile: remove stack selection page

* mobile: require at-least 2 assets to stack

* mobile: sort stack children by fileCreatedAt

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

mobile/lib/modules/asset_viewer/providers/asset_stack.provider.dart

@@ -46,5 +46,6 @@ final assetStackProvider =
       .isArchivedEqualTo(false)
       .isTrashedEqualTo(false)
       .stackParentIdEqualTo(asset.remoteId)
+      .sortByFileCreatedAtDesc()
       .findAll();
 });