CmdPal: Pull out VM bits from ShellPage.xaml.cs (#40479)

ref #40113

Moves a lot of the "model" logic out of `ShellPage.xaml.cs` into
`ShellViewModel`.

The LARGE majority of this code is copy-paste moving code. We're now
using a couple more messages to pass navigation between the VM and the
page. And a couple new messages for passing ETW events.

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Messages/GoHomeMessage.cs

@@ -4,6 +4,7 @@
 
 namespace Microsoft.CmdPal.UI.ViewModels.Messages;
 
-public record GoHomeMessage()
+// TODO! sticking these properties here feels like leaking the UI into the models
+public record GoHomeMessage(bool WithAnimation = true, bool FocusSearch = true)
 {
 }