Rewrite handle-pointer-input.md for WinUI 3

- Update all API references from Windows.UI.Xaml to Microsoft.UI.Xaml
- Update all API links from /uwp/api/ to /windows/windows-app-sdk/api/winrt/
- Replace Windows.UI.Input with Microsoft.UI.Input
- Replace Windows.UI.Colors with Microsoft.UI.Colors
- Update PointerDeviceType from Windows.Devices.Input to Microsoft.UI.Input
- Update code samples to use WinUI 3 namespaces
- Update sample download links for WinUI 3 versions
- Replace archived UWP samples with WindowsAppSDK-Samples links
- Update document date to reflect changes

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Qiutong Shen