Fix UI helper errors during headless -Preset and -Config runs (#4941)

* Make UI helpers no-op when no window exists

The -Preset and -Config paths run Invoke-WinUtilAutoRun before the XAML
form is created and before PresentationCore is loaded, so every call into
Invoke-WPFUIThread failed with InvokeMethodOnNull and every call into
Set-WinUtilTweaksProgressIndicator failed to resolve [Windows.Visibility].
The errors were non-terminating, so tweaks still applied, but each run
filled the log with noise.

Loading presentationframework earlier does not help: Visibility lives in
PresentationCore, which only loads once a WPF object is instantiated, and
the XAML-named progress controls do not exist in these paths either.
Guarding the two helpers covers Invoke-WPFtweaksbutton, Invoke-WPFundoall
and Invoke-WPFFeatureInstall, which the existing per-call-site $hasUI
convention never reached.

* Suppress stray console output from automation runs

Invoke-WPFRunspace returns an IAsyncResult that no caller uses, and
Set-WinUtilRegistry was the only New-PSDrive call site that did not
suppress its output. A GUI click handler discards both, but the -Preset
and -Config paths call the workflows directly, so an async handle dump
and a PSDrive table landed in the user's log.

The handle itself is kept because pester/runspace.Tests.ps1 asserts that
Invoke-WPFRunspace returns a single IAsyncResult, so the suppression goes
at the four call sites reachable from Invoke-WinUtilAutoRun.

* Add project learning for window-free UI helpers

functions/public/Invoke-WPFAppxRemoval.ps1

@@ -96,5 +96,5 @@ function Invoke-WPFAppxRemoval {
             $sync.ProcessRunning = $false
         }
 
-    }
+    } | Out-Null
 }