The `Task.Wait` note should be copied to `Task.WaitAsync`

[antonfirsov]

See dotnet/runtime#114689 (comment).

Also nice to have:

• Improve the visibility of the notes if possible.
• Mention that exceptions may leak to TaskScheduler.UnobservedTaskException .
• The example should demonstrate how to observe and log exceptions.
• The Task.Wait example can be shortened and modernized (eg. why to start a Thread to cancel a CancellationTokenSource ?)

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-threading-tasks