[Enhancement] Combobox

[mou-haz]

fix #185

[NotYoojun]

I noticed that the RestrictToTaskbar attached property in ComboBoxBehaviorHelper was defined but never actually used throughout the codebase. I've removed this unused property to clean up the code.

Verification

I searched the entire codebase and confirmed that:

• No XAML files reference this property
• No C# code calls the getter/setter methods
• The property was only defined but never consumed

@mou-haz Could you clarify the original intention behind this RestrictToTaskbar property? Was this:

1. An incomplete feature that was meant to be implemented later?
2. A leftover from refactoring that should have been removed?
3. Something that was supposed to be used but accidentally missed in the implementation?

If this property was intended to serve a specific purpose, please let me know so we can either:

• Properly implement the missing functionality, or
• Document why it should remain for future use

Otherwise, removing unused code helps maintain a cleaner codebase and reduces confusion for future contributors.

[mou-haz]

@NotYoojun Thanks for the review, As for the RestrictToTaskbar property, in Winui combobox the popup try to not extend beyond the taskbar but rather shift upwards.

winuiCombobox.mp4

This is not yet implemented here. so I agree it should be deleted.