Padding on ItemsView clips items

### Describe the bug

I'm having a horizontal ItemsView that is scrollable. I want the items inset horizontally by 8 points so that they don't hug the window border. But when they are scrolled out of the view, the items should not clip at that 8 point padding, they should expand beyond the padding, and only clip at window edge. This works as expected when using ListView and a horizontal `ItemsStackPanel`

### Steps to reproduce the bug

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Example project: [test.zip](https://github.com/user-attachments/files/20775053/test.zip)

### Expected behavior

The ItemsView does not clip its items at the padding specified

### Screenshots


### NuGet package version

WinUI 3 - Windows App SDK 1.8 Experimental 1: 1.8.250515001-experimental2

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

_No response_

Start by running the linked test.zip example with the shown ItemsView markup and horizontal StackLayout, then compare its scrolling and clipping with the described ListView behavior. Verify that ItemsView Padding="8,0" still insets the items while clipping occurs only at the window edge; the issue is done when the expected scrolling behavior is reproduced and confirmed.

Written by the indexing model from the issue text.