Cmdpal: user research on extension invokes (#43905)

## Summary of the Pull Request

Added two events that Niels asked for:

- `CmdPal_ExtensionInvoked`
- Track which extensions are being used (e.g., file search, app
launching, calculator, etc.).
    - Properties logged
        - ExtensionId - Unique identifier of the extension provider
        - CommandType - Display name of the command being invoked
        - Success - Whether the command executed successfully
        - ExecutionTimeMs - Execution time in milliseconds
- `CmdPal_SessionDuration`
    - Tracks how long Command Palette stays open (launch → close). 
    - Properties logged
        - DurationMs - Session duration in milliseconds
        - CommandsExecuted - Number of commands executed
        - PagesVisited - Number of pages visited
- DismissalReason - Why the session ended (Escape, LostFocus, Command,
etc.)
        - SearchQueriesCount - Number of search queries executed
        - MaxNavigationDepth - Maximum navigation depth reached
        - ErrorCount - Number of errors encountered



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## PR Checklist

- [ ] Closes: #xxx
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [x] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/CommandPaletteHost.cs

@@ -34,6 +34,6 @@ public sealed partial class CommandPaletteHost : AppExtensionHost, IExtensionHos
 
     public override string? GetExtensionDisplayName()
     {
-        return Extension?.ExtensionDisplayName;
+        return Extension?.ExtensionDisplayName ?? _builtInProvider?.DisplayName ?? _builtInProvider?.Id;
     }
 }