Code Quality: Removed ISidebarItemModel 2

[0x5bfa]

Resolved / Related Issues

This is part of the phase 1 mentioned in #17970 (comment)

• Code Quality: Broader SidebarView control usage #15283

Steps used to test these changes

• Check if a section has children
• Check if a section has collapse/expand transition
• Check if items are shown in flyout
• Check if an item can be added at runtime (e.g., pinning an item)
• Check if an item can be right clicked
• Check if an item can be left clicked

[Copilot]

Pull request overview

This PR completes the removal of the ISidebarItemModel interface as part of phase 1 refactoring. The interface is deleted, and its properties (Children, IsExpanded, PaddedItem) are now accessed directly on concrete implementations like LocationItem rather than through the interface.

Changes:

• Removed ISidebarItemModel interface entirely
• Changed INavigationControlItem to no longer inherit from ISidebarItemModel
• Refactored SidebarItem to bind Children, IsPaddedItem properties directly in XAML instead of accessing them through Item.Children, Item.PaddedItem
• Changed SidebarView.SelectedItem from ISidebarItemModel to object type
• Simplified XAML template by using TemplateBinding Children and reusing DefaultSidebarItemTemplate for flyout items
• Replaced HookupOwners and HookupItemChangeListener methods with property change handlers using GeneratedDependencyProperty

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Files.App.Controls/Sidebar/ISidebarItemModel.cs	Deleted the ISidebarItemModel interface
src/Files.App/Data/Contracts/INavigationControlItem.cs	Removed ISidebarItemModel inheritance
src/Files.App/Views/MainPage.xaml.cs	Simplified SidebarControl_ItemInvoked pattern matching
src/Files.App.Controls/Sidebar/SidebarView.Properties.cs	Changed SelectedItem type from ISidebarItemModel to object
src/Files.App.Controls/Sidebar/SidebarStyles.xaml	Updated template bindings to use Children and IsPaddedItem directly, simplified flyout template
src/Files.App.Controls/Sidebar/SidebarItem.cs	Replaced Item.Children references with direct Children property access, added ChildrenFlyout_Opened handler
src/Files.App.Controls/Sidebar/SidebarItem.Properties.cs	Added property change handlers for Children, Owner, and IsInFlyout using GeneratedDependencyProperty
src/Files.App.Controls/Sidebar/SidebarItemAutomationPeer.cs	Updated to access parent.Children directly instead of parent.Item?.Children

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