Port Layout Primitives

```[tasklist]
### Initial Port
- [x] Update namespace (to `CommunityToolkit.WinUI.Controls`)
- [x] Ignore `AdaptiveGridView` for now
- [x] Merge differences from UWP main to
- [x] WinAppSDK
- [x] Uno Platform fork
- [x] Import original doc or setup new doc
- [x] Samples
- [x] Tests
- [x] All brought over tests pass for UWP/WinAppSDK
- [x] Support for WASM via Uno Platform
```

```[tasklist]
### Known Issues / Remaining
- [x] WrapPanel Sample binding doesn't work form ItemsPanelTemplate
- [ ] UniformGrid not working properly in WASM
- [ ] ConstrainedBox sample missing as we don't have TilesBrush yet
- [ ] https://github.com/CommunityToolkit/Windows/issues/130
- [ ] https://github.com/CommunityToolkit/Windows/issues/129
- [ ] https://github.com/CommunityToolkit/Windows/issues/128
- [ ] Tests should be converted to use new test page setup over XamlReader
- [ ] Split StaggaredPanel/Layout doc and samples?
- [ ] https://github.com/CommunityToolkit/Windows/issues/131
```

## Notable Changes

- We didn't bring over `AdaptiveGridView` as it should be replaceable by the `UniformGridLayout` for `ItemsRepeater`

## Open Issues

## Future Improvements

Start with the remaining checklist for the layout primitive samples and tests, especially the UniformGrid WASM issue and the missing ConstrainedBox sample. Review the existing test-page setup rather than the XamlReader approach. Done means the listed remaining items are resolved, including the linked issues and the proposed documentation/sample split.

Vom Indexierungsmodell aus dem Issue-Text verfasst.