[Windows-inflight/10.0.101] Fix Device test failing in the PR 37746

[devanathan-vaithiyanathan]

Issue Details

On Windows, dynamically updating the content of a ContentPresenter can throw a System.ArgumentException when the content contains controls such as RefreshView or ScrollView.

This happens when a platform view is reused while it is still attached to its previous WinUI parent, causing a “PointerEventRouter object already has an owner” exception.

The initial fix detached the platform view from its previous parent, but some scenarios still failed because:

• The logical content was not detached before creating the control-template platform tree.
• ContentPanel.Content = null could leave stale children in CachedChildren.

Description of Change

Updated the Windows ContentViewHandler content-update flow to properly handle direct, templated, and empty content.

• Detach the existing content before creating the template platform tree.
• Added a RemoveFromParent helper to safely detach the incoming platform view without disconnecting its handler.
• Clear ContentPanel.CachedChildren before assigning new content or when the content becomes null.

Issues Fixed

Fixes #37958

Fixed below test cases:
Control.DeviceTests:

• ControlTemplateInitializesCorrectly
• ControlTemplateCanBeReplacedCorrectly
• ContentView updating it's ControlTemplate works
• PropagateContextCorrectly

Core.DeviceTests:

• Content Initializes Correctly
• Content Updates Correctly
• ContentIsSetInitially
• WindowSupportsEmptyPage_Platform

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[kubaflo]

/azp run maui-pr-devicetests

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[kubaflo]

What's the status of this one? Is it ready for review?