Set Command Palette window as the topmost when shown and move to the bottom when hidden (#40444)

## Summary of the Pull Request

Ensures the Command Palette main window is brought to the front and made
topmost when shown. When the palette is hidden (cloaked but not
destroyed), it is moved to the bottom of the window stack to avoid
interfering with the user workflow. Dynamic removal of the topmost flag
is a precaution to prevent the cloak window from bothering user in
accessibility tools that too much -- in case they don't recognize cloak
windows as not visible).

## PR Checklist

- [x] **Closes:** #38726 
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [x] **Tests:** Nothing to test
- [x] **Localization:** Nothing to localize
- [x] **Dev docs:** Nothing to update
- [x] **New binaries:** No new binaries
- [x] **Documentation updated:** nothing to update

## Detailed Description of the Pull Request / Additional comments

## Validation Steps Performed

I've tested that the Command Palette window is display over other
top-most windows (e.g. Task Manager). I've tested that the command
palette is displayed over the Rainbow gadgets when it was originally
under the gadget.

src/modules/cmdpal/Microsoft.CmdPal.UI/MainWindow.xaml.cs

@@ -234,6 +234,10 @@ public sealed partial class MainWindow : WindowEx,
 
         PInvoke.SetForegroundWindow(hwnd);
         PInvoke.SetActiveWindow(hwnd);
+
+        // Push our window to the top of the Z-order and make it the topmost, so that it appears above all other windows.
+        // We want to remove the topmost status when we hide the window (because we cloak it instead of hiding it).
+        PInvoke.SetWindowPos(hwnd, HWND.HWND_TOPMOST, 0, 0, 0, 0, SET_WINDOW_POS_FLAGS.SWP_NOMOVE | SET_WINDOW_POS_FLAGS.SWP_NOSIZE);
     }
 
     private DisplayArea GetScreen(HWND currentHwnd, MonitorBehavior target)
@@ -332,6 +336,10 @@ public sealed partial class MainWindow : WindowEx,
             BOOL value = true;
             PInvoke.DwmSetWindowAttribute(_hwnd, DWMWINDOWATTRIBUTE.DWMWA_CLOAK, &value, (uint)sizeof(BOOL));
         }
+
+        // Because we're only cloaking the window, bury it at the bottom in case something can
+        // see it - e.g. some accessibility helper (note: this also removes the top-most status).
+        PInvoke.SetWindowPos(_hwnd, HWND.HWND_BOTTOM, 0, 0, 0, 0, SET_WINDOW_POS_FLAGS.SWP_NOMOVE | SET_WINDOW_POS_FLAGS.SWP_NOSIZE);
     }
 
     private void Uncloak()

src/modules/cmdpal/Microsoft.CmdPal.UI/NativeMethods.txt

@@ -6,6 +6,8 @@ SetForegroundWindow
 GetWindowRect
 GetCursorPos
 SetWindowPos
+HWND_TOPMOST
+HWND_BOTTOM
 IsIconic
 RegisterHotKey
 UnregisterHotKey