Fix "WebUI 2" typo in "Get started w/ wv2 in WinUI 2 (UWP) apps"

[mitchcapper]

Rendered article section for review:

• Get started with WebView2 in WinUI 2 (UWP) apps > Step 7 - Build and run the project containing the WebView2 control
  • /webview2/get-started/winui2.md
  • Internal preview: https://review.learn.microsoft.com/microsoft-edge/webview2/get-started/winui2?branch=pr-en-us-3502#step-7---build-and-run-the-project-containing-the-webview2-control
  • External preview: https://github.com/mitchcapper/edge-developer/blob/winui2_not_webui2/microsoft-edge/webview2/get-started/winui2.md#step-7---build-and-run-the-project-containing-the-webview2-control
  • Before/live: https://learn.microsoft.com/microsoft-edge/webview2/get-started/winui2#step-7---build-and-run-the-project-containing-the-webview2-control
  • Changed "WebUI" to "WinUI".
    • 0 hits on "webui" in repo.

PR background:

Oops I feel these places are supposed to be WinUI 2 not WebUI 2. WebUI 2 is 100% a developer sdk https://github.com/webui-dev/webui but pretty sure not at all what these docs are talking about:)

WebUI 2.0 is also some random naming MS gave to their new 'edge' UI framework that is purely internal, despite some news sources talking about MS releasing WebUI 2.0 itself:) It however is also not what these docs are referring to. Clearly someone at MS didn't google before writing the press release but that's a separate issue.

Hopefully fixing these things will make it a bit less confusing that WebUI 2 is not a MS thing to use in development with WinUI2.

AB#58299740

[learn-build-service-prod]

Learn Build status updates of commit 426a1ff:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/webview2/get-started/winui2.md	✅Succeeded	View

For more details, please refer to the build report.

[mikehoffms]

LGTM - Writer/Editor.

0 hits in repo on "webui".