Bug: TilesBrush not rendering correctly in WASDK compared to UWP

### Describe the bug

> Is there a known issue with TilesBrush? I copied the code and image from Windows Community Toolkit Gallery app and it doesn't work in a simple app. No error, but nothing displayed.
>
> 

### Steps to reproduce

```text
I was able to repro this bug in a blank WASDK app, and found that this issue is present in the WASDK version of the Gallery as well.

[TilesBrushWasdkBugTest.zip](https://origin.owlcore.io/ipfs/bafkreibvihky53onnwf5yezaujf6rv3jdsy4wbckeqhdrqck6s4oi3tk24?filename=TilesBrushWasdkBugTest.zip)
```

### Expected behavior

On Wasdk, we see:


It's not clear why this works on UWP but not Wasdk.

On UWP, we see:


### Screenshots

_No response_

### Code Platform

- [ ] UWP
- [x] WinAppSDK / WinUI 3
- [ ] Web Assembly (WASM)
- [ ] Android
- [ ] iOS
- [ ] MacOS
- [ ] Linux / GTK

### Windows Build Number

- [ ] Windows 10 1809 (Build 17763)
- [ ] Windows 10 1903 (Build 18362)
- [ ] Windows 10 1909 (Build 18363)
- [ ] Windows 10 2004 (Build 19041)
- [ ] Windows 10 20H2 (Build 19042)
- [ ] Windows 10 21H1 (Build 19043)
- [ ] Windows 10 21H2 (Build 19044)
- [ ] Windows 10 22H2 (Build 19045)
- [ ] Windows 11 21H2 (Build 22000)
- [ ] Other (specify)

### Other Windows Build number

_No response_

### App minimum and target SDK version

- [ ] Windows 10, version 1809 (Build 17763)
- [ ] Windows 10, version 1903 (Build 18362)
- [ ] Windows 10, version 1909 (Build 18363)
- [ ] Windows 10, version 2004 (Build 19041)
- [ ] Windows 10, version 2104 (Build 20348)
- [ ] Windows 11, version 22H2 (Build 22000)
- [ ] Other (specify)

### Other SDK version

_No response_

### Visual Studio Version

_No response_

### Visual Studio Build Number

_No response_

### Device form factor

_No response_

### Additional context

Reported in the [`#community-toolkit`](https://discord.com/channels/372137812037730304/669640275500466197/1373160624686895216) channel in the Windows App Community.

### Help us help you

Yes, I'd like to be assigned to work on this item.

Start by running the attached TilesBrushWasdkBugTest.zip in a blank WinAppSDK/WinUI 3 app and compare it with the Windows Community Toolkit Gallery's WASDK and UWP examples. Trace the TilesBrush rendering entry point and reproduce the difference; done means TilesBrush displays the expected tiled image in WASDK as it does in UWP, with a regression check if the project provides one.

Scritto dal modello di indicizzazione a partire dal testo della issue.