Create JumpList in background thread to improve performance (#6985)

* Perform JumpList creation in background thread to improve performance when pwsh owns the window (i.e. when the Jumplist has to be created)

* Move JumpList creation to a later stage to allow for more code that might make it exit earlier as suggested in PR review by @iSazonov

src/Microsoft.PowerShell.ConsoleHost/WindowsTaskbarJumpList/TaskbarJumpList.cs

@@ -12,7 +12,8 @@ namespace Microsoft.PowerShell
     {
         internal static void CreateElevatedEntry(string title)
         {
-            // check startupInfo to know if the current shell owns a window before proceeding
+            // Check startupInfo first to know if the current shell is interactive and owns a window before proceeding
+            // This check is fast (less than 1ms) and allows for quick-exit
             GetStartupInfo(out StartUpInfo startupInfo);
             var STARTF_USESHOWWINDOW = 0x00000001;
             var SW_HIDE = 0;

src/Microsoft.PowerShell.ConsoleHost/host/msh/ConsoleHost.cs

@@ -26,6 +26,7 @@ using System.Management.Automation.Language;
 using Dbg = System.Management.Automation.Diagnostics;
 using ConsoleHandle = Microsoft.Win32.SafeHandles.SafeFileHandle;
 using System.Management.Automation.Tracing;
+using System.Threading.Tasks;
 #if LEGACYTELEMETRY
 using Microsoft.PowerShell.Telemetry.Internal;
 #endif
@@ -120,10 +121,6 @@ namespace Microsoft.PowerShell
             }
 #endif
 
-#if !UNIX
-            Microsoft.PowerShell.TaskbarJumpList.CreateElevatedEntry(ConsoleHostStrings.RunAsAdministrator);
-#endif
-
             // put PSHOME in front of PATH so that calling `powershell` within `powershell` always starts the same running version
             string path = Environment.GetEnvironmentVariable("PATH");
             if (path != null)
@@ -214,6 +211,16 @@ namespace Microsoft.PowerShell
                     return ExitCodeBadCommandLineParameter;
                 }
 
+#if !UNIX
+                // Creating a JumpList entry takes around 55ms when the PowerShell process is interactive and
+                // owns the current window (otherwise it does a fast exit anyway). Since there is no 'GET' like API,
+                // we always have to execute this call because we do not know if it has been created yet.
+                // The JumpList does persist as long as the filepath of the executable does not change but there
+                // could be disruptions to it like e.g. the bi-annual Windows update, we decided to
+                // not over-optimize this and always create the JumpList as a non-blocking background task instead.
+                Task.Run(() => TaskbarJumpList.CreateElevatedEntry(ConsoleHostStrings.RunAsAdministrator));
+#endif
+
                 // First check for and handle PowerShell running in a server mode.
                 if (s_cpp.ServerMode)
                 {