Add deprecation notice to WebView2 WinUI 2 (UWP) getting-started article

[GrantMeStrength]

Article

https://learn.microsoft.com/en-us/microsoft-edge/webview2/get-started/winui2

Issue

The article provides correct step-by-step instructions for creating a WebView2 app in WinUI 2 (UWP), but it presents this as a viable path for new development without any deprecation or migration notice.

As of 2025–2026:

• UWP is officially deprecated and in maintenance mode. Microsoft recommends WinUI 3 / Windows App SDK for all new projects.
• WebView2 on WinUI 2 UWP has known limitations (no autofill UI, no default printing, limited API surface compared to Win32/WinUI 3).
• The article does not link to or recommend the WinUI 3 (Windows App SDK) equivalent getting-started guide for new projects.

Suggested fix

Add a prominent note/banner at the top of the article, such as:

Note: UWP is in maintenance mode. For new projects, we recommend using Get started with WebView2 in WinUI 3 (Windows App SDK) apps instead. This guide is for maintaining existing WinUI 2 (UWP) apps.

Additional context

• The NuGet package version reference ("2.8.0 or later") is acceptable — latest stable is 2.8.7.
• The procedural steps and code samples are still technically correct.
• The companion platform page (webview2/platforms/winui2-uwp.md) already notes some limitations but doesn't clearly state the deprecation of the overall UWP platform.