[Windows] Fix for MenuFlyoutItems programmatically added to MenuFlyoutSubItems are not visible

[Tamilarasan-Paranthaman]

Root Cause of the issue

• If the parent PlatformView of MenuFlyoutSubItem is MenuBarItem, it does not retrieve the items in the Reset method of the MenuFlyoutSubItemHandler on Windows. As a result, it is null, and subsequent item insertions are not processed.

Description of Change

• Add a condition to check if the PlatformView is a MenuBarItem. If it is, retrieve the items and process the remaining logic in the Reset method of the MenuFlyoutSubItemHandler on Windows and works fine

Issues Fixed

Fixes #26856

Tested the behaviour in the following platforms

• Windows
• Android
• iOS
• Mac

Screenshot

Before Issue Fix	After Issue Fix
MenuFlyoutItemsIssue.mp4	MenuFlyoutItemsFix.mp4

[dotnet-policy-service]

Hey there @Tamilarasan-Paranthaman! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Redth]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[mattleibow]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[mattleibow]

LGTM

Pity there is no base type or interface, but I assume WinUI is not getting more menu item types anytime soon. :)

[PureWeen]

• failing test is unrelated