Fixed [Windows] TabbedPage current page indicator can be wrong

[NanthiniMahalingam]

Issue Details

• When selecting the last page in a TabbedPage and leaving the TabbedPage using the PopModalAsync method to navigate to the main page, reloading the TabbedPage with a new instance causes the selected indicator to not update properly.

Root cause

• The NavigationView's selected item is not set to null when leaving the TabbedPage using the PopModalAsync method after selecting a page. As a result, the selected indicator for the previous page is not removed properly.

Description of Change

• Invoked the OnHandlerDisconnect method when leaving the TabbedPage and set the NavigationView's selected item to null.

Validated the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

Fixes #26069

Output

Before	After
Before_fix.mp4	After_fix.mp4

[dotnet-policy-service]

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

[jsuarezruiz]

/azp run

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[jsuarezruiz]

/azp run

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