`WebView2WpfBrowser` references preview features even when building for stable APIs

[ssrmm]

The WebView2WpfBrowser sample references various APIs related to the "SaveAs"-UI unconditionally even though those are only available in preview builds of the Microsoft.Web.WebView2 NuGet package. In particular in MainWindow.xaml.cs and SaveAsDialog.xaml.cs. This means that Debug Stable APIs and Release Stable APIs cannot be built against stable versions of the Microsoft.Web.WebView2 NuGet package.

Steps to reproduce:

1. Change version of Microsoft.Web.WebView2 to a stable one.
2. Build the sample.

Actual Behavior:

• Several compile errors related to "SaveAs"-APIs.

Expected Behavior:

• No compile errors
• Expirimental "SaveAs"-APIs are hidden behind USE_WEBVIEW2_EXPERIMENTAL, like other experimental APIs already are.

[Master-Ukulele]

@ssrmm Thanks for telling us, unfortunately, there's a little gap between public Github version wpf sample app and release/prerelease. For now, in your app or the local wpf sample app, as workarounds, please hide it with the USE_WEBVIEW2_EXPERIMENTAL, remove its usage if you don't need, or switch to the prerelease package. Read more at our release note