Remove Monarch/Peasant & Make UI single-threaded (#18215)

As before, a minor refactor:
* I started off by removing the Monarch/Peasant with the goal of moving
  it into and deduplicating its functionality with `WindowEmperor`.
* Since I needed a replacement for the Monarch (= ensures that there's
  a single instance), I wrote single-instance code with a NT mutex
  and by yeeting data across processes with `WM_COPYDATA`.
* This resulted in severe threading issues, because it now started up
  way faster. The more I tried to solve them the deeper I had to dig,
  because you can't just put a mutex around `CascadiaSettings`.
  I then tried to seeif WinUI can run multiple windows on a single
  thread and, as it turns out, it can.
  So, I removed the multi- from the window threading.
* At this point I had dig about 1 mile deep and brought no ladder.
  So, to finish it up, I had to clean up the entire eventing system
  around `WindowEmperor`, cleaned up all the coroutines,
  and cleaned up all the callbacks.

Closes #16183
Closes #16221
Closes #16487
Closes #16532
Closes #16733
Closes #16755
Closes #17015
Closes #17360
Closes #17420
Closes #17457
Closes #17799
Closes #17976
Closes #18057
Closes #18084
Closes #18169
Closes #18176
Closes #18191

## Validation Steps Performed
* It does not crash ✅
* New/close tab ✅
* New/close window ✅
* Move tabs between windows ✅
* Split tab into new window ✅
* Persist windows on exit / restore startup ✅

build/scripts/New-UnpackagedTerminalDistribution.ps1

@@ -34,7 +34,7 @@ Param(
 )
 
 $filesToRemove = @("*.xml", "*.winmd", "Appx*", "Images/*Tile*", "Images/*Logo*") # Remove from Terminal
-$filesToKeep = @("Microsoft.Terminal.Remoting.winmd") # ... except for these
+$filesToKeep = @() # ... except for these
 $filesToCopyFromXaml = @("Microsoft.UI.Xaml.dll", "Microsoft.UI.Xaml") # We don't need the .winmd
 
 $ErrorActionPreference = 'Stop'

build/scripts/Test-WindowsTerminalPackage.ps1

@@ -58,7 +58,7 @@ Try {
 
     ### Check the activatable class entries for a few DLLs we need.
     $inProcServers = $Manifest.Package.Extensions.Extension.InProcessServer.Path
-    $RequiredInProcServers = ("TerminalApp.dll", "Microsoft.Terminal.Control.dll", "Microsoft.Terminal.Remoting.dll", "Microsoft.Terminal.Settings.Editor.dll", "Microsoft.Terminal.Settings.Model.dll", "TerminalConnection.dll")
+    $RequiredInProcServers = ("TerminalApp.dll", "Microsoft.Terminal.Control.dll", "Microsoft.Terminal.Settings.Editor.dll", "Microsoft.Terminal.Settings.Model.dll", "TerminalConnection.dll")
 
     Write-Verbose "InProc Servers: $inProcServers"