EffectiveViewportChanged using Scroll Ports from other windows

[will-velazquez]

Describe the bug

It seems that when the EffectiveViewportChangedArgs are calculated, they are taking into account scroll ports from other windows. This causes all of the args to be incorrectly constrained as if the windows were overlapping each-other.

Sample repro available at https://github.com/will-velazquez/effective-viewport-bug

Steps to reproduce the bug

1. Create a window with a noop EffectiveViewportChanged handler on any of its element
2. Create a second window with an EffectiveViewportChanged handler on one of its elements
3. Resize the original window to be smaller than the second window
4. EffectiveViewPortChanged handler is called on the second window, and the values given are wrong

Expected behavior

Each window should track its scroll ports separately

Screenshots

From running https://github.com/will-velazquez/effective-viewport-bug

https://github.com/user-attachments/assets/2f7f4b92-273b-4343-a376-f1e27ddea3ef

NuGet package version

WinUI 3 - Windows App SDK 1.6.1: 1.6.240923002

Windows version

Windows 11 (22H2): Build 22621

Additional context

No response