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

---------

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

mobile/lib/modules/home/models/selection_state.dart

@@ -4,33 +4,38 @@ class SelectionAssetState {
   final bool hasRemote;
   final bool hasLocal;
   final bool hasMerged;
+  final int selectedCount;
 
   const SelectionAssetState({
     this.hasRemote = false,
     this.hasLocal = false,
     this.hasMerged = false,
+    this.selectedCount = 0,
   });
 
   SelectionAssetState copyWith({
     bool? hasRemote,
     bool? hasLocal,
     bool? hasMerged,
+    int? selectedCount,
   }) {
     return SelectionAssetState(
       hasRemote: hasRemote ?? this.hasRemote,
       hasLocal: hasLocal ?? this.hasLocal,
       hasMerged: hasMerged ?? this.hasMerged,
+      selectedCount: selectedCount ?? this.selectedCount,
     );
   }
 
   SelectionAssetState.fromSelection(Set<Asset> selection)
       : hasLocal = selection.any((e) => e.storage == AssetState.local),
         hasMerged = selection.any((e) => e.storage == AssetState.merged),
-        hasRemote = selection.any((e) => e.storage == AssetState.remote);
+        hasRemote = selection.any((e) => e.storage == AssetState.remote),
+        selectedCount = selection.length;
 
   @override
   String toString() =>
-      'SelectionAssetState(hasRemote: $hasRemote, hasMerged: $hasMerged, hasMerged: $hasMerged)';
+      'SelectionAssetState(hasRemote: $hasRemote, hasMerged: $hasMerged, hasMerged: $hasMerged, selectedCount: $selectedCount)';
 
   @override
   bool operator ==(covariant SelectionAssetState other) {
@@ -38,10 +43,14 @@ class SelectionAssetState {
 
     return other.hasRemote == hasRemote &&
         other.hasLocal == hasLocal &&
-        other.hasMerged == hasMerged;
+        other.hasMerged == hasMerged &&
+        other.selectedCount == selectedCount;
   }
 
   @override
   int get hashCode =>
-      hasRemote.hashCode ^ hasLocal.hashCode ^ hasMerged.hashCode;
+      hasRemote.hashCode ^
+      hasLocal.hashCode ^
+      hasMerged.hashCode ^
+      selectedCount.hashCode;
 }